WO2009047277A1

WO2009047277A1 - System and method for detecting document alteration

Info

Publication number: WO2009047277A1
Application number: PCT/EP2008/063495
Authority: WO
Inventors: Steven Gerardus Tuinstra
Original assignee: Security Transfer B.V.
Priority date: 2007-10-11
Filing date: 2008-10-08
Publication date: 2009-04-16
Also published as: GB0719864D0; GB2453568A

Abstract

A system and method fordetecting alteration of documents having a photoluminescent security layer. The methodcomprises forming a low resolution photoluminescence image of the document revealing irregularities in the photoluminescent security layerduring transportation of the document past a photoluminescence scanner,storing the photoluminescence image andanalysing the photoluminescence image to determine whether the irregularities actually correspond to alterations made to the original document.By storing images, the analysis of the images may be performed even if the original document is no longer easily retrievable. This is particularly important in the context of clearing cheques.

Description

SYSTEM AND METHOD FOR DETECTING DOCUMENT ALTERATION

BACKGROUND OF THE INVENTION

1. Field of the Invention

[0001] The present invention relates generally to methods of detecting fraud and more particularly to the detection of fraudulent alterations to original documents such as cheques, bank drafts and the like. Such a method may be integrated into the clearing process of such documents. The invention also relates to a system suitable for detection of such fraud, in particular for integration with other equipment used for document clearing.

2. Description of the Related Art [0002] Devices for examining and determining the authenticity of valuable documents and papers are well known in the art. In general, such devices rely upon the presence of authenticating features of the documents themselves. If such security features are not detected, then there is a possibility that the document has been counterfeited. As the technical possibilities to produce counterfeit documents becomes greater, there is an ever increasing need to make the security features more difficult to copy. To this end, modern bank notes and other documents such as passports and identity cards use UV images, holograms, watermarks, micro-images, texture and the like to improve security. As a consequence of such measures, the scrutinizing of the documents requires ever finer and more complex detection and scanning facilities. The time and memory space required to perform a complete analysis of a given document and compare it with a master document are also increased accordingly.

[0003] An example of a device for security checking of documents is described in US Publication No. 2006/0062427. According to that publication, the entire document is initially recorded by an image sensor at a resolution of around 250 dpi. This resolution is suggested as sufficient for determining the type of document being checked. After initial determination, a sequence of different image recordings and high-resolution recordings for high-security features may be made. By limiting the high resolution recordings to specific regions of the document, the overall time and data transfer for the security check is reduced.

[0004] The present invention relates to another category of document fraud, i.e. alteration fraud, which does not require counterfeiting of the document, as it is committed on the original document itself. Alteration of original documents such as cheques involves making changes to the original manuscript or to variable data provided on the document. For a cheque, this may involve changing the name of the payee or altering the amount. For other documents, other changes may be applicable. In the case of original documents, scrutiny and comparison with a master document is not helpful, since each document is effectively unique and since the authenticating features will likely not have been tampered with.

[0005] A method of improving the security of original documents (in particular documents such as cheques) is described in WO97/26615. Variable data such as the amount of the cheque and payee information is not only filled in on the appropriate fields of the cheque, but also printed on the cheque in an encrypted form, such as a numeric value. Alterations to the filled in data can be detected by comparing that data to the encrypted data. However, this method does not provide a solution for the vast majority of cases where the cheque is filled in and used without the opportunity to encrypt and securely print the filled in data on the cheque.

[0006] A further method of improving the security of original documents is described in PCT publication No. WO2004/045864. According to the disclosure, a security paper comprises a photo-luminescent substance that lights up in response to UV excitation. The paper is provided with a thin coating that is at least partially impervious to such excitation. Any damage to the coating is visible under UV illumination since the photo-luminescence of the paper beneath is revealed. The disclosure suggests using a detection element sensitive to the emitted radiation to produce a detection signal. A microprocessor compares the signal to a reference value to determine whether falsification or forgery has occurred. While such comparisons allow for automatic fraud evaluation, this method has certain disadvantages. One important disadvantage lies in the fact that the light values do not resemble the visual appearance of the actual alterations. As a consequence, there remains a need to visually inspect the suspect physical cheque in order to determine whether or not an alteration has actually occurred and if so, the nature, form and size of the alteration. Within the tight time limits of today's high volume cheque clearing process it has become increasingly difficult (and in many cases impossible) to timely retrieve, transport, inspect and return the suspect physical cheques in order to execute such visual inspection. This is particularly the case, if at some point in the cheque processing cycle the physical cheque is taken out of the process ("truncated") and replaced by an electronic image of that same cheque. This so-called "cheque truncation" process is increasingly becoming international standard practice in today's clearing systems.

[0007] A method of inspecting a security document is also disclosed in patent application No. GB 2283607. According to one embodiment of that disclosure, the possibility of using ultraviolet illumination is discussed in which a security paper such as a bank cheque is scanned with both visible light and non- visible light. Bit maps of both images are then compared, while the bit map of one or both of the images is also used for numerical recognition processing. In another embodiment, verification and value recognition take place at the non- visible wavelength. In both cases it is understood that the images are produced at a resolution sufficient for numerical recognition processing. This requires significant data capture and processing capacity, especially in the case of high-speed operation. Data compression is suggested for speeding up comparisons. It is also suggested that not all pixels in a data set may be compared. However, if a sample is found to fall below a predetermined authenticity confidence level and thus qualifies as a potential fraud, it is suggested that further processing takes place at a higher resolution. As a consequence, data capture and processing capacity limitations are still an issue of concern.

[0008] Thus, there is a particular need for a system that overcomes some or all of the above- mentioned drawbacks and is suitable for automated detection of alterations to cheques and other original documents.

BRIEF SUMMARY OF THE INVENTION

[0009] The present invention addresses these problems by providing a method for detecting alteration of original documents of the type having a photo luminescent security layer. The method comprises transporting the document past a photoluminescence scanner, forming a low resolution photoluminescence image of the document or part thereof revealing irregularities in the security layer, storing the photoluminescence image and analysing the image to determine whether the irregularities actually correspond to alterations made to the original document. Photoluminescence is a process in which a chemical compound absorbs a specific wavelength range of electromagnetic radiation (excitation), and subsequently emits electromagnetic radiation of a different wavelength: the emission radiation. The appearance revealed by such emission is considered to be the photoluminescence appearance of the document. Forming a photoluminescence image refers to forming a record enabling reproduction of a visual representation of this photoluminescence appearance. Consequently, in the present context a photoluminescence image refers to said record and/or said visual representation. The photoluminescence image may be formed while the document is passing through a document transport device such as a cheque reader sorter. This makes it possible to integrate the fraud detection method into the existing cheque clearing process without causing disruptions or delays. By storing the image, the analysis of the images may be made subsequently and repeatedly, even if the original document is no longer easily retrievable or even in the case that the document has been destroyed. This is particularly important in the context of clearing cheques and the like, since cheques may be received at a first location and the images may be analysed only after having been submitted to the payer's bank for clearing. By analysing a photoluminescence image at a low resolution it is possible to reveal alterations on the cheque in a way that better enhances their detection. The photoluminescence image can replace the physical cheque in the phase of visual evaluation of suspect cheques. It will also be understood that the forming, the storage and the analysis of the images need not be performed in that particular order and can be part of a reiterative process.

[0010] Despite the aforementioned advantages, a photoluminescence image is by no means a logical candidate to serve as a fraud analysis object. Even with high levels of UV illumination, the radiation emitted by photoluminescence is limited by the saturation level of the chemical compound involved. At best, the intensity of the radiation emitted will be around 3 orders of magnitude (100Ox) lower than that from an image that is well illuminated by light in the visible region. Due to the low light availability, it is very difficult - and in many cases even impossible - to form a sharp image when the target is moving. Prior thinking considered a sharp image as necessary to be able to effectively detect all types of alteration fraud, in particular the very subtle ones. This was in line with a general tendency to increase resolution for the detection of document fraud. This is described, for instance, in the aforementioned US Publication No. 2006/0062427, according to which an image with a resolution of 250 dpi is used to identify the document, after which a high resolution image is formed in order to be able to evaluate the presence and completeness of security features belonging to that document. Also the aforementioned patent application GB 2283607 teaches that an optional higher resolution processing is applied if the regular image falls below a preset authenticity confidence level and thus deserves closer inspection. According to the present invention it has surprisingly been found that despite the aforementioned disadvantage, a low-resolution photo luminescence image of a moving document is nevertheless a suitable candidate to serve as an alteration fraud analysis object.

[0011] While a resolution of 100 dpi or less may be suitable for many purposes, the resolution will preferably be lower than 50 dpi and even more preferably around 25 dpi. The unaided human eye can perceive frequencies of up to approximately 50 periods per degree of the vision field, corresponding to approximately 250 dpi on a document at a distance of 30 cm. Consequently, typical document clearing scanners use a scanning frequency of lower than 300 dpi, since more detail exceeds the perception of the human eye and is thus irrelevant. Such scanners also use a frequency of at least 100 dpi, since it is known that below such a resolution, relevant detail of handwriting and printed type is lost. It has however surprisingly been found that using a low resolution image of 100 dpi or less than 100 dpi (preferably less than 50 dpi and most preferably around 25 dpi) even very small alterations to a document of the type having a photo-luminescent security layer may be detected. This surprising finding is based on the insight that even a very subtle alteration to an original text that can not be distinguished by the human eye from the remaining original text surrounding it, will always cause a larger irregularity in the photo-luminescent security layer than the original text. The replacing data that is added in the alteration process increases the size of the irregularities even further. Such coarser irregularities will show up under excitation of the security layer and subsequently in the photo-luminescent emission image that is formed. A low resolution image will act as a filter that suppresses the original text and enhances the alterations. [0012] The low resolution photoluminescence image may be formed in real time i.e. at the same speed in which document image capturing takes place in a typical cheque clearing process, with limited photo-luminescent emission and is a suitable object for the effective evaluation of even very subtle alterations to that document. Furthermore, the use of such lower definition requires fewer resources in terms of both scanning and subsequent storage and analysis of the image. [0013] According to a further embodiment of the invention, the photoluminescence image comprises a number of pixels, each formed by adding up the values of a plurality of smaller pixels. By this so-called pixel binning, a lower resolution image may be formed if the document is originally scanned at a higher definition. Pixel binning is particular useful in conjunction with the formation of an image based on light emitted from a photo-luminescent surface. Since the available light emitted from such a surface is generally limited, pixel binning may increase the gain of the image and improve the signal to noise ratio. The photoluminescence image may be initially formed at a definition of e.g. 100 dpi and the above process of pixel binning may be used to reduce the definition to an even lower definition of e.g. 25 dpi, thus increasing the gain sixteen- fold. A similar binning procedure may be used to reduce the definition from 80 dpi to 20 dpi. The skilled person will be well aware that any suitable method having a similar effect of lowering the resolution of the image is considered to fall within the scope of the term "binning".

[0014] According to a still further embodiment of the invention, the method may comprise forming a second image of the document under illumination by visible light. This second image can be the regular clearing image as commonly used in today's cheque clearing systems. As mentioned above, the clearing images are normally captured at 100 to 300 dpi. The provision of the two images allows both the regular clearing image and the image based on the security layer to be readily compared. In many cases, the act of writing onto a cheque will disrupt the security layer. In that case, the regular image will closely correspond to the photoluminescence image. If the original manuscript has been altered and original text has been removed or replaced, the images will not correspond to the same extent. According to another aspect of the invention, the analysis may additionally comprise comparing at least part of the photoluminescence image with at least part of the second image. Thus the analysis may compare the whole image or only those parts of the image where manuscript text is present (or has been removed or replaced) as recorded by the photoluminescence image. Any parts of the photoluminescence image above a certain threshold that are not retrieved in the second image may thus cause a processor to indicate a discrepancy which can then be reported or marked for further investigation. In the context of the present invention, it is preferred that the analysis takes place electronically in an automated procedure. Nevertheless, other forms of analysis of the photoluminescence image, e.g. inspection by an operator, may additionally or alternatively take place.

[0015] Additionally or alternatively, the analysis may comprise image enhancement of the low resolution photoluminescence image by filtering and selection of the lower frequency ranges. Removal of original text by masking, erasing or the like will generally lead to a coarser photoluminescence image. Disturbances in the low frequencies are thus an important fraud indicator and isolating these specific frequencies may be a preferred aspect of image enhancement. This can be done by binning as described above. Low frequencies can also be isolated from the image by performing a two dimensional Fourier transform of the image, and subsequently removing the high frequency components, leaving only the low frequency components containing the indication of fraud, and then applying the inverse Fourier transform to re-build an image that is understandable to humans. Alternative methods to achieve the same effect include various types of linear convolution filters, where for each pixel a new value is found by calculating a specific influence of its surrounding pixels, e.g. gaussian filters and low pass filters, and binary morphology filters that are able to isolate groups of pixels meeting certain similar criteria, e.g. erosion and dilation algorithms. The skilled person will be well aware that any suitable algorithm, procedure or device having a similar effect may be applied to isolate the low frequencies and is considered to fall within the scope of the term "filtering". Image enhancement may also include other procedures e.g. contrast manipulation. Following image enhancement, the analysis of the photoluminescence image may also include segmentation. In segmentation, special algorithms can be used to localize and measure disturbances by e.g. thresholding, local thresholding and edge detection. Subsequently these disturbances can be classified, thus providing an indicator of fraud probability. Analysis of only the photoluminescence image may lead to sufficient information to provide an alert. Alternatively, both images may be subjected to Fourier analysis and the results compared.

[0016] In a preferred embodiment, as a result of the analysis, an indicator can be positioned on e.g. the photoluminescence image, corresponding to a position of a possible alteration. Such an indicator may be an arrow or circle around the region of interest that may draw an operator's attention to the location of possible fraud, or a highlighting or any other indication of such a location. The indicator may of course also be provided on the second image. [0017] In a further preferred embodiment, at least part of the photo luminescence image and the second image are displayed simultaneously. By simultaneously displaying the photoluminescence and second images a trained operator at a distinct location may easily compare the images e.g. by overlaying one onto the other. [0018] According to a preferred embodiment of the method, the security layer comprises a substance that is photoluminescent to UV radiation. Such a substance is preferably excited by radiation in the 350-400 nm band and emits luminescence in the visible band at preferably 450 nm or higher. Nevertheless, although such a layer and image forming procedure is preferred, it is understood that other alternative detection and security provisions may be provided based on alternative security layers including opaque coatings as described in WO2004/045864 and alternative frequency ranges. Furthermore, any appropriate manner may be used to incorporate the photoluminescent substance into the document. Thus the skilled man will readily understand that the photoluminescent substance may be included in the paper as part of the pulp or size or may be provided on the surface of the document or part thereof as a coating or printed layer or for example as a pattern or a grid. Of significance is that irregularities are formed in the security layer of the original document on addition and/or alteration of manuscript or printed text and that such irregularities are visible in the photoluminescence image. The method of forming the photoluminescence image may use any form of photoluminescent radiation, including but not limited to those based on UV and IR excitation. The image may be detected on the same side of the document as the radiation source or from the opposite side.

[0019] Preferably, the document is a cheque. In this context, a cheque is understood to be a printed money transfer form or similar instrument instructing a financial institution to pay a third party. The cheque is ultimately presented to the payer's bank for redemption. Most preferably, the method is performed automatically and at least the photoluminescence image is formed on transporting the cheque through a cheque processing machine, e.g. a cheque reader sorter. Because of the advantages outlined above, the scanning speed may be above 15 centimetres per second. Preferably, the photoluminescence scanner and the scanner that forms the regular clearing image are both located in the same cheque transport device, in order to avoid an extra pass to form the photoluminescence image. [0020] The invention also relates to a system for performing the methods as described above. The system may comprise a photo luminescence scanner for forming a photo luminescence image of the document or part thereof revealing irregularities in a security layer, a transport device for transportation of the document past the photo luminescence scanner, a memory for storing the photoluminescence image and a processor for analysing the photoluminescence image to determine whether the irregularities correspond to alterations made to the original document. In general the photoluminescence image will be formed in a scanning procedure in which the document moves with respect to a linear detection head but other embodiments are possible. Such a detection head may be based on any suitable detection principles e.g. using charge coupled devices (CCD) or contact image sensors (CIS).

Nevertheless, the terms scanning and scanner are intended to cover other image capturing devices such as those in which a matrix of points or pixels are detected simultaneously, as in the case of a digital photograph. The process of forming the image may have intermediate resolution stages. Reference to the resolution of the device is understood to be the resolution in which the image is ultimately formed and/or analysed. Furthermore, the term "processor" is understood to encompass any suitable means for analysing the image, including but not limited to: a single computer or microprocessor provided with appropriate software; a distributed system where certain processing tasks are performed by different devices or at different and remote locations; and hardware only arrangements provided with filters or the like. Similarly, the term "memory" is intended to encompass any suitable memory means capable of storing the image in any form, temporarily or permanently, including but not limited to electrical, optical, magnetic, chemical and charge based devices.

[0021] The transport device may be a conventional cheque or note feed device using rollers, bands, belts, air flow or the like. Preferably the device has a transport or scanning speed of more than 15 centimetres per second. In particular, it may be desirable that the system according to the invention is integrated into a conventional document or cheque handling device, in which also the regular clearing image is formed. For local desktop or intermittent use a device having a capacity of more than 50 documents per minute is preferred. For centralised systems, a device having a capacity of more than 500 documents per minute may be preferred. [0022] Preferably, the scanner comprises a UV light source operating at around 350-400 nm and an image capturing device susceptible to light emitted by photoluminescence from the original document in the visible region. The UV light source may be an LED emitting in the required region or any other suitable source. Preferably the excitation radiation does not contain radiation in the emission wavelength range. Such radiation could reflect off the document and thus disturb the capturing of the specific photoluminescence emission wavelength by the scanner. For this reason, the excitation source may be arranged in such a way that it delivers the appropriate wavelengths only. This can be achieved by filtering out all other wavelengths, e.g. by using a coloured glass or interference filter. In a preferred embodiment this is achieved by using a mirror that reflects the appropriate wavelength only, and transmits all other wavelengths. It is also important that the excitation radiation is focussed onto the area that is scanned to achieve the required intensity while minimising excess heat production. This can be achieved by using a lenticular lens which may even double as a coloured glass filter if it is made of the appropriate material. In a preferred embodiment the radiation is focussed by a curved mirror that also serves as the filtering mirror.

[0023] The photoluminescence scanner is arranged to form images of 100 dpi or less than 100 dpi, preferably less than 50 dpi, and more preferably around 25 dpi. A second scanner may also be provided for forming an image under illumination by visible light. The resolution of the second scanner will be at least 100 dpi, since this is generally the lowest resolution that is fit to produce an image of the document that is adequately legible for document clearing purposes.

[0024] The photoluminescence scanner may be designed so that appropriate adjustment may be arranged to lower the resolution of the captured image. One suitable arrangement is to form an image comprising a number of pixels, each formed by adding up the values of a plurality of smaller pixels. In that case pixel binning is used to emulate the behaviour of a low resolution scanner. In both a true low resolution scanner and this emulated low resolution scanner, the linear resolution is decreased with a factor X, the pixel size is increased with the square of X, and thus the amount of light captured by that surface is also increased by the square of X. Thus, the effect of pixel binning in forming the image is analogous to joining multiple capturing elements in the scanner itself into larger capturing elements. [0025] The processor is arranged to analyse the photo-luminescence images at a resolution of 100 dpi or less than 100 dpi, preferably of less than 50 dpi and most preferably around 25 dpi. Preferably, the processor is arranged to compare at least part of the photoluminescence image and the second image and may also utilize e.g. a Fourier analysis algorithm for analysing a frequency distribution of pixels forming the photoluminescence image or even both images according to the image analysis methods as described above.

[0026] The system may also comprise a display for displaying the photoluminescence and/or second image and the processor may be arranged to locate an indicator on one of the images, at a position corresponding to a possible alteration as detected according to the above described analysis, or similarly highlight or enhance the area of interest. Although the system is described as comprising a display, it will of course be understood that the display may be located at a remote station. Software located in the processor or at the remote station may assume the role of driving the display. It will also be understood that at least part of the processor that performs the analysis of the document can also be located at a remote station. As described above, the display and its driving software may be arranged to display photoluminescence and second images simultaneously. Appropriate manipulation of the images may also be provided, in particular allowing overlaying, zooming, resolution reduction, brightness control, rotation etc. In addition to or instead of the display, an appropriate printout or other visualisation of the images and related data may be provided. [0027] Another aspect of the invention comprises a software program product embodying at least the analysis method as described above. The program may be run on the processor of a single dedicated device comprising scanning and analysing capabilities. Alternatively, the software may be distributed over different locations: the scanning may take place at a first location; storage of the photoluminescence image may be at a second location; automated analysis may take place at a third location; and display and visual analysis may take place at a yet further location. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The features and advantages of the invention will be appreciated upon reference to the following drawings which show certain exemplary embodiments of the invention, in particular: [0029] FIG. 1 is a schematic view of a first embodiment of the invention;

[0030] FIG. 2 is a perspective view of an exemplary cheque including a security layer;

[0031] FIGS 3 - 9 show different views of an exemplary sample document and image under analysis

[0032] FIG. 10 is a schematic view of a device according to a second embodiment of the invention; and

[0033] FIG. 11 is a perspective view of an exemplary UV source according to a further aspect of the invention.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

[0034] The following is a description of an embodiment of the invention, given by way of example only and with reference to the drawings. Referring to FIG. 1, a device 100 for individual hand feed of documents for detection according to the invention is shown. The device is arranged for desk-top use and may have typical dimensions of around 120 mm wide, 280 mm long. The device comprises a single item feeder 1 leading to a transport mechanism comprising a plurality of rollers 2 for transporting individual cheques along a transport path 22 through the device 100. The device further comprises a magnetic ink character recognition

(MICR) reader head 20, UV lamp 3, a photo luminescence scanner 4, a rear image scanner 5, a front image scanner 6, and an output pocket 20, arranged sequentially along the transport path 22.

[0035] The photoluminescence scanner 4 is a CIS device in near direct contact with the object to be scanned. Such a CIS device consists of a linear array of detectors, covered by a focusing lens and in the described example having a resolution of 80 dpi and being sensitive to visible light above 450 nm. The photoluminescence scanner 4 also comprises a frame grabber that prepares the images as frames and bins them to a resolution of 20 dpi. The rear image scanner 5 and front image scanner 6 are also CIS devices having a definition of 150 dpi and operating across the full visible light spectrum from 420 nm to 650 nm. They are provided with their own visible light source for illumination of the object to be scanned. The skilled person will nevertheless be aware that alternative scanning devices having different principles of operation and resolutions may also be used without departing from the scope of the invention.

[0036] Also schematically shown in FIG. 1 is a computer 25, comprising a processor 24, memory 26 and display 28. The processor 24 is connected to the device 100 by suitable means to control and receive information from the various components. Details of such connection and control will not be elaborated at present but will be evident to the skilled person in the light of the description. Although the processor 24, memory 26 and display 28 are shown as local to the device 100, it will be immediately evident to the skilled person that these items may also be remotely located. Furthermore, at least certain of the items may be duplicated, thus processors, memories and displays may be located remotely at e.g. a plurality of receiving banks, each of which may be provided with its own analysis software allowing analysis and display of results according to the requirements of the individual establishment.

[0037] FIG. 2 shows detail of a cheque 29. Although reference is made to a cheque, it will be understood that this also encompasses other documents having a photoluminescent security layer. Cheque 29 comprises a paper layer 30 onto which, information regarding the document is printed during its production. The information may include the name of the bank 32, the name of an account holder or payer 34 and security or electronically readable markings such as MICR code 36 written using a standard font with magnetically detectable ink. The paper layer 30 is covered by a thin security coating 38 that has been applied at a final stage in the production of the cheque. The coating 38 comprises a photo-luminescent substance being sensitive to excitation by radiation of wavelengths in the 350 to 400 nm region. In response to such excitation, the photo-luminescent substance emits visible light in the visible wavelength region above 450 nm. The information 32, 34, 36 carried on the paper layer 30 is thus clearly visible through the security coating 38. Cheque 29 has been written by a user and carries manuscript information relating to an amount of payment, the payee and the signature of the payer. This writing 40 has been applied onto the security coating 38 and may at least partially disrupt it to penetrate to the paper layer 30 below thus forming an irregularity in the security coating 38. Also shown in FIG. 2 is an alteration 44. A portion of the writing 40 has been removed by careful scraping with a scalpel blade. Removal of the writing 40 has also removed a portion of the coating 38 revealing the paper layer 30 below resulting in a further irregularity.

[0038] Operation of the system according to the invention will now be described with reference to FIGS 1 and 2. In use, the transport rollers 2 individually feed a cheque 29 from the feeder 1, along the transport path 22. The transport rollers 2 are adapted to feed the cheque through the device 100 at a transport speed of around 25 cm/s. The cheque 29 is fed past the MICR reader head 20, the scanners 4, 5, 6 and finally to the output pocket 7. As the cheque 29 passes the MICR reader head 20, the MICR code 36 is read and passed to the processor 24. On passing the photo luminescence scanner 4 it is illuminated by UV lamp 3. Since the writing 40 has partially disrupted the coating 38, these areas will have a lower level of photoluminescence and show darker. In the area of alteration 44, the paper layer 30 has also been completely exposed and a minimum level of photoluminescence will be emitted. The photoluminescence scanner 4 is located opposite to the UV lamp 3 and captures the photoluminescence image at 80 dpi from the photo luminescent radiation being emitted from the rear surface of the cheque 29. It will be understood that this arrangement is a preferred embodiment and that the scanner 4 and UV lamp 3 could also both be located at the same side of the cheque 29. Although in the illustrated embodiment the whole cheque 29 is scanned, it will be understood that the device may be arranged to only scan or otherwise process relevant portions of a given document on which security information is to be found.

[0039] Once the photoluminescence image has been captured, the frame grabber of scanner 4 bins the image to 20 dpi, assembles it into a frame and sends it to the computer 25. Lowering the resolution of the image prior to sending is advantageous in reducing the required data transmission capacity.

[0040] As the cheque 29 subsequently passes the image scanners 5, 6, it is illuminated by visible light and scanned to produce a detailed gray scale image having a resolution of 150 dpi.

[0041] The processor 24 receives the data transmitted by scanner 5 and 6, it analyses the data from the MICR reader head to read MICR code 36 which provides information relating to the issuing bank and stores these data as a document record. The image formed by the scanner 4 is transmitted to the processor 24 also.

[0042] The processor 24 analyses the images formed by the scanner 4 to determine whether possible alterations to the cheque 29 have occurred, and outputs its findings as a fraud risk index. This may be done using the method shown in FIGS 3 to 9. The processor includes an indicator on the photo luminescence image at the location of the alteration. Both the fraud risk index and the photoluminescence image with the indicator superimposed are included in the document record. The images can be displayed on display 28 and may be scrutinised by a human operator by simultaneously viewing both the photoluminescence and visible images. This can take place during scanning but may also take place subsequently.

[0043] FIGS 3 to 9 show further views and different scanned images of a portion of a sample document 50 of the type described in relation to FIG. 2. The document 50 has been subjected to alteration. The manner in which processor 24 can determine such alteration will be described. [0044] FIG. 3 shows the document 50 including three manuscript versions of a word 51 , 52, 53. According to FIG. 4, portions of the words 51, 52, 53 have been removed. The word 51 has been altered by erasing with a solvent. The second word 52 has been partially covered with correction fluid. Part of the third word 53 has been carefully scratched away with a scalpel. The missing portions of the words 51, 52, 53 have then been replaced with a different text such that the overall meaning of the word is changed. This is shown by FIG. 5, which shows a conventional scanned image of the document 50 as would be produced by the scanners 5, 6 of FIG. 1. FIG. 6 shows a photoluminescence image produced under UV illumination of the document 50 at a definition of 250 dpi corresponding to that of FIG. 5. This image is formed for illustration purposes showing the actual visible image of the irregularities in the security coating 38 as revealed by photoluminescence. As can be seen from FIG. 6, the alterations to the words 51, 52, 53 are clearly visible as a result of the removal of the photo-luminescent security coating 38 and exposure of the paper 30 below. As can also be seen from FIG. 6, the security coating 38 has not been applied all over the document 50 but only to those areas where variable data that may be subject to fraudulent alteration is to be added. [0045] FIG. 7 and FIG. 8 show photoluminescence images of the document 50 at lower resolution levels than in FIG. 6. In FIG.7 the image has been taken at a resolution of approximately 150 dpi. The original words 51, 52, 53 are still visible. In FIG. 8, the resolution has been reduced to the level of 30 dpi. At this resolution, the original text is no longer visible yet the alteration remains clear. According to FIG. 9 the image has been yet further enhanced by applying filtering techniques well known to the skilled person to remove the grey scales present in FIG. 8. At this point, only the image due to the alteration remains. The filtering used to arrive at the image of FIG. 9 may be performed using various principles of image enhancement. One method is by binning, involving the forming of the larger pixels by adding up the values of a plurality of smaller pixels, thus creating a lower resolution image. Low frequencies can also be isolated from the image of FIG. 8, by performing a two dimensional Fourier transform of the image, and subsequently removing the high frequency components, leaving only the low frequency components containing the indication of fraud. Thereafter the inverse Fourier transform is applied to re-build an image that is understandable to humans. Alternative methods to achieve the same effect include various types of linear convolution filters, where for each pixel a new value is found by calculating a specific influence of its surrounding pixels, e.g. Gaussian filters and low pass filters, and binary morphology filters that are able to isolate groups of pixels meeting certain similar criteria, e.g. erosion and dilation algorithms. The skilled person will be aware that any suitable algorithm having a similar effect may be applied to isolate the low frequencies from an initially captured low-resolution image. Image enhancement may also be applied to achieve the image of FIG. 9, including e.g. contrast manipulation. Following image enhancement, the next step is segmentation. In segmentation, special algorithms are used to localize and measure the disturbances, e.g. thresholding, local thresholding and edge detection. Subsequently these disturbances are classified, thus providing an indicator of fraud probability.

[0046] An alternative reader sorter device 200 for high volume processing of cheques is shown in FIG. 10. The device is intended to be freestanding and may have a length of around 2600 mm and a width of around 600 mm. The device 200 is adapted for processing cheques at a volume of up to 2000 items per minute and is provided with a feeder unit 8 into which a stack of cheques 29 are placed. A single item feeder 9 is also provided for bypass use. A plurality of transport rollers 10 guide the cheques 4 along a track 11 past a plurality of stations including TDI camera 12, UV source 13, MICR reader head 14, rear image scanner 15, front image scanner 16, front endorser 17 and rear endorser 18. The cheque is thereafter sorted to multiple output pockets 19. Also shown is an external computer 25, similar to that of FIG. 1, including processor 24, memory 26 and display 28. [0047] UV source 13 is based on LED technology and will be described in further detail below. It will however be understood that other suitable sources of UV radiation could be used. TDI camera 12 serves as a highly sensitive form of photo luminescence sensor using Time Delay and Integration (TDI). TDI is a method of scanning in which a CCD line scanner produces an image of a moving object by means of a stack of linear arrays aligned with and synchronized to the movement of the object to be imaged. As the object moves from one line of the array to the next, the photoelectric charges on the lines of the CCD chip are continuously moved to the next adjacent line and accumulated. This results in a longer effective exposure time without introducing additional motion blur. In this manner TDI camera 12 can provide higher gain at low light levels than is possible with a conventional line scanner, providing the speed of the charge movement is exactly the same as the object speed. Such a TDI camera 12 has been found most suitable for high speed operation as a photo luminescence scanner.

[0048] MICR reader head 14, rear image scanner 15 and front image scanner 16 are generally conventional and may correspond to the devices described in relation to FIG. 1. Endorser printers 17 and 18 print an endorsement (additional printed data) onto the cheque 29 as the cheque is being transported to the output pockets 17.

[0049] In use, the device 200 operates in a similar manner to the device 100 of FIG. 1 and for the sake of expediency, only the significant differences will be described. Under control of the processor 24, feeder unit 8 supplies cheques 29 which are carried by transport rollers 10 along track 11. Rollers 10 are designed for high volume operation and are capable of transporting up to 2000 documents per minute at speeds of around 5 m/s. The front and rear surfaces of the cheques 29 are read by TDI camera 12, MICR reader head 14, rear image scanner 15 and front image scanner 16 and the captured images and data are transmitted to the computer 25 for analysis and storage in the form of a document record. Based on the data received, the processor 24 controls front endorser 17 and rear endorser 18 to print a suitable endorsement onto the cheque 29 for subsequent identification. The cheque 29 is thereafter sorted according to a further signal received from the processor 24, to one of the multiple output pockets 19. The contents of each pocket 19 may be subsequently sent to the bank in question or even destroyed according to the rules of operation adopted by that bank. It will be understood that, since the device 200 is designed to process up to 2000 cheques per minute, a human operator would be unable to view and scrutinise all of the cheques. For this reason, processor 24 analyses the captured images and data and determines whether there is a likelihood that fraud has occurred. This determination may be based on various algorithms both for image analysis as described in relation to FIGS 3 - 9 and also based on profiling of e.g. the cheque value, payee, payer etc. Based on the determination, the processor 24 may display items from the document record on the display 28 and draw these to the attention of a human operator. As discussed elsewhere, such analysis, determination and display may also take place at a remote location and even on different or multiple computers.

[0050] FIG. 11 shows a schematic view of the UV source 13 of FIG. 10. It will however be understood that such a source may also be used in the device 100 of FIG. 1. According to a further aspect of the invention, UV source 13 comprises a strip 62 provided with an array of encapsulated LEDs 64 emitting primarily in the UV region of 360-380 nm. In order to achieve maximum utilisation of the light output from the LEDs 64, the encapsulation provides an initial focus to achieve beams 66, each with a spread of around 30°. Arranged in line with beams 66 is a curved, UV cold mirror 68. Mirror 68 is effectively transparent to light above 380 nm and reflects light having shorter wavelengths. Although LEDs 64 are designed to emit in the 360-380 nm range, the emission is not limited to this range and is effectively emitted in a Gaussian distribution over a wider range. Due to the limited amount of light produced by photo luminescence, it is important that none of the longer wavelength visible light in beams 66 is directed towards the TDI camera 12 (or other form of photo luminescence detector) as it could interfere with the detection. The mirror 68 thus acts as an effective filter to remove these unwanted wavelengths. In addition to its function as a filter, mirror 68 also acts to focus the remaining light into a focussed beam 70 that is directed towards the cheque 29.

[0051] Thus, the invention has been described by reference to the embodiment discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art. For example, the analysis carried out by the processor 24 may include multiple levels of signal analysis including spectral analysis of the images to detect deviations from expected values or deviations of the photoluminescence image from the visible images. Furthermore, probability values for detecting a possible alteration may be linked to other factors e.g. the value of a cheque or the payee. Flagged cheques may be retained for evidentiary purpose while other cheques may be destroyed. Furthermore, while the system has only been described in relation to detection of cheque alteration, it is clear that such a system could be integrated into existing systems for fraud detection. Further modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method for detecting alteration of an original document having a photoluminescent security layer, comprising: transporting the document past a photoluminescence scanner; forming a photoluminescence image of at least part of the document at a resolution of 100 dpi or less, revealing irregularities in the security layer; storing the photoluminescence image; and analysing the photoluminescence image to determine whether the irregularities correspond to alterations made to the original document.

2. The method according to claim 1, wherein the transportation speed of the document is more than 15 centimetres per second.

3. The method according to claim 1, wherein the transportation speed of the document is more than 50 centimetres per second.

4. The method according to any preceding claim, wherein the photoluminescence image is formed at a resolution of less than 100 dpi.

5. The method according to any preceding claim, wherein the photoluminescence image is formed at a resolution of less than 50 dpi.

6. The method according to any preceding claim, wherein the photoluminescence image is analysed at a resolution of less than 50 dpi.

7. The method according to any preceding claim, wherein the photoluminescence image comprises a number of pixels, each formed by adding up detected values of a plurality of smaller pixels.

8. The method according to any preceding claim, wherein the analysis is performed automatically in a processor.

9. The method according to claim 8, wherein the analysis comprises image enhancement of the photoluminescence image by filtering and selection of the lower frequency ranges .

10. The method according to any preceding claim, further comprising forming a second image of the document under illumination with visible light.

11. The method according to claim 10, wherein a photoluminescence image and the second image are both formed during the same step of transporting the document.

12. The method according to claim 10 or claim 11, wherein the analysis additionally comprises comparing at least part of the photoluminescence image and the second image.

13. The method according to any of claims 10 to 12, wherein the photoluminescence image and the second image are displayed simultaneously.

14. The method according to any preceding claim, wherein the photoluminescence image and/or the second image further comprises an indication of a possible alteration by means of an indicator.

15. The method according to any preceding claim, wherein the security layer comprises a substance that is photo-luminescent when excited by UV radiation and the photoluminescence image to be formed is based on the photoluminescent emission of said substance.

16. The method according to any preceding claim, wherein the document is a cheque.

17. A system for detecting alteration of an original document having a photoluminescent security layer, comprising: a photoluminescence scanner for forming a photoluminescence image of at least part of the document with a resolution of 100 dpi or less for revealing irregularities in the security layer; a transport device for transportation of the document past said photoluminescence scanner; a memory for storing the photoluminescence image; and a processor arranged to analyse the photoluminescence image to determine whether the irregularities correspond to alterations made to the original document.

18. The system according to claim 17, wherein the transport device is arranged to transport the document at more than 15 centimetres per second.

19. The system according to claim 17, wherein the transport device is arranged to transport the document at more than 50 centimetres per second.

20. The system according to any of claims 17 to 19, wherein the photo luminescence scanner comprises a UV light source and the photoluminescence image is formed based on the photo-luminescence of the document to the UV radiation.

21. The system according to any of claims 17 to 20, wherein the photoluminescence scanner is arranged to form an image with a resolution of less than 100 dpi.

22. The system according to any of claims 17 to 20, wherein the photoluminescence scanner is arranged to form an image with a resolution of less than 50 dpi.

23. The system according to any of claims 17 to 22, wherein the processor is arranged to analyse the photoluminescence image at a resolution of around 25 dpi.

24. The system according to any of claims 17 to 23, wherein the photoluminescence scanner is arranged to detect emission values at a plurality of smaller pixels and add up the values of a number of the smaller pixels to form larger pixels.

25. The system according to any of claims 17 to 24, wherein the processor utilizes a Fourier analysis algorithm for analysing a frequency distribution of pixels forming the photoluminescence image.

26. The system according to any of claims 17 to 25, further comprising a second scanner for forming a second image of the document under illumination with visible light.

27. The system according to claim 26, wherein the transport device is arranged to transport the document past both the photoluminescence scanner and the second scanner.

28. The system according to claim 26 or claim 27, wherein the processor is additionally arranged to compare at least part of the photoluminescence image and at least part of the second image.

29. The system according to any of claims 26 to 28, wherein the system comprises a display arranged to display the photoluminescence image and the second image simultaneously.

30. The system according to any of claims 17 to 29, comprising a display for displaying at least part of an image of the document and wherein the processor is arranged to provide an indication of a possible alteration by means of an indicator on the image.

31. A software program product comprising instructions for performing the method of analysis as defined in any of claims 1 to 16.

32. A software program product comprising instructions for performing the method of analysis as defined in any of claims 1 to 16 when loaded onto the processor in a system according to any of claims 17 to 30.