GB2270586A - Fingerprint verification system - Google Patents

Abstract

A fingerprint verification system is used as a fast and effective security device to verify that an applicant to a service protected by the system is authorized to use the system. Electronic information allowing the creation of a correlation filter on a spatial light modulator (SLM) 26 is input from a smart card 10 or fingerprint database. The fingerprint or cluster of fingerprints of the applicant are then correlated through the SLM 26 in order to derive a comparison with those electronically stored. Although the system uses electronically stored pattern information, the correlation is performed optically. <IMAGE>

Description

FINGERPRINT VERIFICATIQN SYSTEM Background of the Invention 1. Field of the Invention This invention relates to a fingerprint verification device, 2. Description of Related Art The roots of optical processing go back to the last century when Ernst Abbe performed some pioneering research.

Coherent optical pattern recognition has been studied since its introduction by Anthony Sander Lugt in 1964 (see Vander Lugt, A., Signal Detection by Complex Spatial Filtering IEEE Transactions on Information Theory, vol.IT-1O no. 2 p.139, Apr 1964). This important step was made possible by the development of both a powerful coherent light source (the laser, in 1961) and off axis holography, by Leith and Upatnieks, also in 1964. Prom, this time to the present, optical techniques for pattern recognition have been known to be extremely powerful because of their speed, high discrimination powers, and noise immunity.

The fundamental phenomenon upon which optical correlators rely is the natural ability of a lens to extract a two dimensional Fourier transform of an input signal. The speed at which the lens will perform the transformation is independent of the input signal or object; a complex input is processed just as fast as a simple one. The computation is done completely -in parallel, and occurs literally at the speed of light This speed reprosents the most significant advantage that optical processors have over digital devices, and is the reason why so much research has been conducted in this field. Optical devices based on the transformation properties of a lens are commonly referred to as Fourier optical signal processors.

Unfortunately, optical correlation devices suffer from some severe practical difficulties which have prevented them from becoming useful in the real world. In order to exploit the processing speed of the optical technique, input data must be introduced at an extremely high rate, and of course the output must be removed just as fast. Furthermore, in order to compare one pattern with another, a reference or target pattern must be input as well. This reference data is input in the form of a correlation filter, and must be physically located at the transform plane of the correlator. These two input requirements necessitate fast, high resolution devices which can compete with the information bandwidth capabilities of modern digital hardware.

This data transfer problem has always presented a significant bottleneck in Fourier optical signal processing devices. However, this problem is not relevant in applications where high speed, high volume data processing is not a necessity.

Fingerprint verification is just such an application. In fingerprint verification a device reads recorded information about a reference fingerprint pattern and uses this information to determine or verify that the reference pattern and an input pattern belong to the same individual. There is no requirement to compare a fingerprint with a large number of reference patterns, nor is there any need to compare many input patterns with a single reference. A single input pattern must be compared with a single reference pattern, or possibly with a small number of reference patterns. Previous attempts at optical fingerprint pattern verification using Fourier techniques have made use of holographic matched filter (HMF) as the correlation filter. The is istypically processed on a card which is carried by the user.

However, a disadvantage of optical processing systems which does affect fingerprint verification utilising a RMF as the correlation filter is that the position and orientation of the correlation filter is extremely critical to the correct operation of the system, This positional tolerance is on the order of microns, and the rotational orientation must be within one or two degrees of the optimal position. The mechanical positioning problem is therefore extremely difficult, requiring high resolution devices and extremely accurate alignment techniques.

Further, a serious systemic disadvantage is the inflexibility imposed by the holographic matched filter. The necessity of having a holographic matched filter precludes the possibility of transferring filter data by any means other than the physical transport of the original or its copies (which must be fabricated optically as well) The matched filter must be physically present in the frequency plane of the correlator, and there is currently no electronic device which will provide the resolution required to represent a holographic matched filter.

This invention seeks to overcome drawbacks of known fingerprint pattern recognition devices.

Summary of the Invention According to the present invention, there is provided a fingerprint verification device comprising the following: a source of light for providing an illuminating beam along a beam path; input means located in the beam path including means to receive at least one fingerprint of an individual {either by the individual placing his finger(s) on the input means or by placing a fingerprint(s) recording in the input means) for modulating the beam with data from at least one fingerprint to form an information beam; optical Fourier transform means in the beam path for providing a Fourier transform of the information beam in a transform plane; a spatial light modulator fixed in said transform plane; a card reader for reading encoded data from a card representing a correlation filter to be written to said spatial light modulator, means for receiving said encoded data from said card reader and for writing a correlation filter to said spatial light modulator in accordance with said encoded data; verification means in the beam path at the output of said spatial light modulator for sensing a correlation signal which is the transform of the product between the Fourier transform of à reference fingerprint(s) which is derived from filter information contained on a card and written to the spatial light modulator, and the Fourier transform of the fingerprint(s) input.

According to another aspect of the invention, there is provided a method of generating a correlation filter for the fingerprint verification device comprising the steps of: forming a correlation filter from each of said at least two fingerprints of an individual which said input means is designed to receive; superposing each said formed correlation filter to record a correlation filter.

According to another aspect of the invention there is provided a method of generating a correlation filter for the fingerprint verification device comprising the steps of: recording a correlation filter from a cluster of all of said at least two fingerprints of an individual which said input means is designed to receive.

Brief Description of the Drawings In the drawings which illustrate example embodiments of the invention: figure 1 is a schematic diagram of a verification device made in accordance with this invention; and figure 2a, 2b and 2c are schematic views which illustrate alternate optical correlation arrangements.

Detailed Descri tion of the Preferred Embodiments In overview, recognising that the filter positioning problem could be solved by permanently fixing and aligning the filter in the#proper position at the transform plane, a spatiaL light modulator (SD() is introduced into the transform plane and is fastened there at the time of manufacture Correlation filters can then be electronically written onto the SLM, avoiding the need to mechanically position and align a filter for every correlation operation.

An electronically addressable filter in a correlator allows filter design and calculation to be carried out electronically with a computer. This fact alone makes the verification system far superior to one which utilizes a standard holographic matched filter. Computer generated filters need not be recorded using holographic techniques, which require sophisticated equipment such as lasers and vibration controlled environments. Holographic matched filters require a holographic--capable recording medium, and finally a stable filter medium which when fixed onto a card to be carried by the user must be able to withstand the rigours of wallets and purses, hot sunlight, freezing temperatures, and spilt coffee and alcoholic beverages.Storing the filter in a digitally encoded form permits the use of cards carrying encoded data, such as "smart cards", or central databases for filter data storage and retrieval.

Computer generated filters can be far more flexible in the. types of operations which can be performed on an input.

These filter algorithms can be very difficult if not practically impossible to implement optically (holographically). The various filter implementations can optimize the behaviour of the correlator with respect to noise erformance, distortion invariance, and discrimination sensitivity Thi# iS accomplished through careful analysis of the recognition problem to be solvede The filter algorithm can then be tuned to the particular input, conditions, and application.

Fingerprint verification is extremely well suited to this application's specific tunability of the computer generated filter. The device has only to compare two sets of fingerprint patterns, and will not be required to differentiate between other types of objects. This allows the filters to be optimized to operate on specific characteristic features of fingerprint patterns which will provide the maximum amount of discrimination.

Distortion and noise characteristics can be studied and accounted for in the filter.

The introduction of an SLM upon which a correlation filter is written opens up a far broader range of useful applications, and makes the system realizable with current technology. The electronic filter data representation permits easy communication of the data from one location to another, and eliminates the severe problems associated with recording, manufacturing, alignment, and reliability of holographic matched filters.

The verification is performed through a hybrid optical/slectronic correlation device. The actual correlation is performed optically, while the correlation signal is analyzed electronically. The ability to read stored reference pattern information is made possible through the introduction of a spatial light mbdulator (SLM) at the filter plane of the optical correlator.

In practice, with reference to figure 1, a subscriber (an authorized user of a service which utilizes the fingerprint verification technology) inserts her card 10 into the fingerprint verification device (the verifier) 20, enabling the encoded fingerprint filter information to be transferred by a reader 22 from the card to the processor 24. This unique information is used by the processor to create an optical filter which is transferred onto the SLM 26, which is contained within the verification device 20. The subscriber then places her fingers on the input screen 28 of the verifier, and the system performs an optical correlation operation, which compares the subscriber's .fingerprint(s) with those represented by the encoded fingerprint information stored on the subscriber's card.The output from the SLM is an optical signal whose characteristics depend on the degree of correlation between the input and reference fingerprints. This optical signal, after passing through lens 34 -and onto the optical detector 36 where its intensity distribution is detected by the optical detector 36, is analyzed by the processor 24 which decides whether the output signal represents a sufficient correlation to indicate a match between the input and reference signals. x positive verification results in the processor 24 allowing the subscriber access to the desired service.

The verification procedure will occur very quickly, on the order of one second or less. The time will be primarily taken up by the various electronic system which make up the device. The optical correlation operation' will occur in several nanoseconds (several millionths of a second), the time required for light to travel from the input to the output plane.The verification operation should take no more time than is currently required by systems requiring users to enter PINs (personal identification numbers ) . This makes the device practical and acceptable as a commercial security.. system for consumer applications such as automated bank teller (ArM) machines and point of sale credit and debit card machines, while providing tremendously improved security against unauthorized use of such services. The high discrimination capability of Fourier optical pattern recognition techniques will ensure accurate verification.

The encoded representation of the filter information enables the incorporation of a card as an integral component of the security system. Encoded information on a card provides a reliable and readable storage medium for the reference pattern information, The same card can also carry information relevant to the services and privileges which the particular card entitles the holder.

The pattern verification is carried out by an optical correlator indicated generally at 38 and which comprises lenses 32 and 34, along with the SLM 26 and a detector 36.

Alternatively, the lenses could be replaced by holographic optical elements which also perform a Fourier transform. The method by which the fingerprint patterrl is introduced to the correlator 38 is dependent on the input system, indicated generally at 29 The function of the input systent is to generate a high contrast, noise and distortion free image of a live fingerprint(s) pattern and deliver it to the input of the optical correlator 38. The input system 29 may be an all--optical system or a hybrid opto--electronic system which would consist of image capture and display devices.The electronic system has the added capabilities of introducing previously recorded and stored input patterns as well as preprocessing of the input pattern. As illustrated in figure 1, the input system 29 comprises one or more lasers 30 along with an expander lens 31 and a collimator lens 33 to illuminate a prism 35 with a beam 37. One face of the prism forms the input screen 28. In an alternative input system, laser 30 may be replaced with an incoherent light source.

An optical correlator requires some degree of coherence in the optical signal as it passes through the system. Coherence is described in terms of spatial and temporal characteristics, and' assumes a significant degree of polarization of the light.

Spatial coherence describes how light at one point on a plane perpendicular to the optical axis correlates in phase to light at another point on the plane. Temporal coherence relates the correlation of light at one point in space but at different Points in time. If a broad band optical source is utilized, then spatial and temporal coherence can be controlled by using source encoding and/or diffraction gratings respectively. Multichannel coqralators use a diffraction grating to spatially isolate each wavelength at the filter plane.An alternative to a white light source is a series of lasers, each with a unique wavelengtbr which provides the advantage of higher spectral power. Tha SL#,, based correlator described here will function with any of ghe possible light sources which are acceptable for Fourier optical: processing devices.

An all--optical input system will utilize the principle of total internal reflection (TIR) to read the pattern formed by the furrows of the input fingerprint pattern. A furrow will create an air space over the surface of a glass screen, allowing light which is internally reflecting from the interior surface of the screen to proceed unimpeded. Ridges, however, will be in contact with the surface, where they will scatter and absorb a portion of the illuminating light. This effect is known as frustrated total internal reflection (FTIR), When the TIR light signal is observed, the primary signal will be due to the furrow pattern.

If the scattered light from the ridge pattern is observed, there may be significant advantages in terms of noise immunity from latent fingerprints. The scattered light signal will be weaker than the TIR signal from the furrows. Despite this cost in illumination efficiency, the improved signal to noise ratio (SNR) of the FTTR signal from the ridges will most likely result in improved performance of the verification system in a real world environment.

For both of the preceding all--optical input schemes, the light signal from the input pattern enters the optical correlator directly, without further interference or signal conditioning from any active electronic devices The alternative to the all--optical input system is an electronic imaging and display system which captures the image of the input pattern and displays it on a device such as an si#a.

The; image capture may be performed by an optical array detector, scanner or similar device. The image can then be displayed at the input of the optical correlator 38 by illuminating the display device, either in transmission or reflection. This scheme permits preprocessing of the input pattern. Preprocessing can provide added flexibility and power to an optical processor.

Alternatively, an optically addressable SLM can be used at the correlator input. This type of device allows a spatial pattern of light on one side of the SLX to affect the reflectivity on the other. Optically addressable SLMs are commonly used in optical signal processing devices to perform incoherent to coherent light conversion.

Input pattern illumination for the electronic imaging and display input may be the same as for the all--optical scheme; TIR or FTIR could be exploited to create a high contrast image of the pattern.

The optical signal carrying the fingerprint pattern information proceeds into the correlator 38 and is transformed by the Fourier transform lens 32. Such a lens will perform an optical transform of the input pattern and display the transform at the Pourier transform plane of the correlator. The Fourier transform plane is typically located at the focal plane of the transform lens 32.The SLM 26 is positioned at the transform plane, and the optical transform of the input pattern passes through the SLM, A correlation filter is written onto the S; modulating the optical transform through a multipLicative operation with the function represented on the S# The second Fourier transform lens 34 is positioned in such a way that the output of the SLM is re--transformed, resulting in the display of a correlation signal at the output plane of the correlator.

The correlation signal represents the transform of the product between the correlation filter written to the spatial light modulator - i.e., the reference fingerprint represented by the data read from the card 10 - and the Fourier transform of the fingerprints of the subscriber at the input screen 28. The correlation signal is usually accompanied by DC, convolution, and noise signals. These additional signals and their relative strengths depend on the correlator architecture and the filter characteristics.

The actual function represented on the SLM for correlation with a reference pattern can be arrived at through numerous methods, and they are described by various names indicating their particular attributes. This flexibility is in fact a tremendous advantage of electronic filter calculation.

Whatever the algorithm, all the filters are designed to produce a correlation signal at the output of the correlator.

An array detector 36 at the output plane plane of the correlator intercepts the correlation signal, converting it to its electronic analog. This electronic signal is then captured, stored and analyzed by the processor 24 (electrotiic electronic the computer) Through analysis analysis of specific characteristics of the correlation signal the processor decides whether or not there is sufficient correlation between the input and reference patterns to warrant C-'! a p?sitive- verification The decision of the processor may be signaled to a host system, which then takes the appropriate action.

The SLM is a device which can spatially modulate (in two dimensions) the amplitude and/or phase of light in either transmission or reflection. The spatial resolution of an SLM varies widely and depends on the type of SLM. SLMs can be divided into two main categories, optically addressable and electrically addressable. In the optically addressable SLM (OASLM) a pattern of light (coherence is irrelevant) is written onto the device, imposing an associated spatial modulation of a second (coherent) beam of light. In the electrically addressable SLM (EASLM) the magnitude of modulation of individual cells or pixels are controlled electrically, with each pixel having its own unique address.

Of particular interest is the liquid crystal television or display (LCTv). These devices are widely used as flat panel displays for portable computers and calculators, control panel displays on equipment and instrumentation, and as video and projection display devices for small televisions and projectors.

LCTVs are relatively inexpensive, have satisfactory spatial resolution, and can be made to modulate light in amplitude and/or phase. LCTVs have proven themselves to be mass producible and reliable, and have minimal power requirements Current technology does not provide the optical system designer with an SDN possessing the spatial resolution capabilities of a holographic recording emulsion, but the resolution is sufficient for correlation operations in an optical data processing device. however, the low spatial resolution results in a low diffraction efficiency, while the information content required to implement a classical matched filter, even with a 128 x 128 pixel SLM, is not small.Advances in filter algorithms has resulted in superior approaches to filter implementations which do not simply attempt to implement a low resolution holographic matched filter.

It must be noted that a holographic matched filter employs a carrier frequency (created by the reference beam) to encode the complex amplitude informatioz on an amplitude only format. This encoding scheme stores both amplitude and phase information, which naturally requires a high information storage capacity from the medium, i.e. high resolution. If the filter modulates only the phase of the light, not only is the efficiency improved (there are no absorption losses in this case), but the information content is substantially reduced. Such a filter is called a phase only filter (POF), and has been shown to perform as well or even better than a matched filter.

Even further savings in data storage can be had if the filter function is hinarized. This process converts a continuous phase function into a two level function. There are once again numerous algorithms for binarizationf but the data storage requirements can be seen to be extremely minimal. Such a filter is called a binary phase only filter (POP), and has also been shown to perform extremely well in spite of the reduced iu' information content.

A significant advantage of the StM as a filter is the flexibility afforded by its ability to rapidly change filters without mechanically replacing the filter. An SLM can therefore be incorporated into the correlator and aligned at the time of manufacture, avoiding the difficulty of mechanically aligning a ZMF in the transform plane at every verification operation.

Holographic filter alignment is known to be very critical for correct operation of a HMF correlator, requiring precision on the order of microns. This places a tremendously high emphasis on the mechanical accuracy and reliability of a positioning system.

The operation of the SLM can be in amplitude, phase, or full complex (amplitude and phase) modulation. The modulation can also be in binary form, as opposed to continuous modulation.

Binary modulation,. as previously stated, has the advantage of greatly reduced data storage requirements.

Another advantage of the SLM--based correlator is that the design and fabrication of the filter can be performed electronically, introducing far more flexibility in filter design. A computer generated filter (CGF) can implement operations which can be very difficult or practically impossible to perform with an optically recorded filter. This makes filter design and testing much faster and more effective. For example, the SLM can compensate for any misalignment in the fingerprint on the input screen of the verifier. This may be accomplished by electronically rotating the filter on the fixed SLM. The actual degree of misalignment does not need to be known since the filter on the SLM may be electronically rotated until the maximum output signal is found. Alternatively, the filter on the SLM could be made rotationally invariant.Furthermore, the pattern on the filter may be electronically made larger or smaller to accommodate scale changes of the input fingerprint. Modern digital techniques permit preprocessing of the reference fingerprint pattern to optimize the correlators performance in terms of expected noise and input distortions. Significant advances in filter algorithms provide the system designer with a large number of starting points from which to start developing an application specific filter.

Electronic or digital storage of the reference fingerprint filter information avoids the practical difficulties associated with holographic recordings and recording media which must be dealt with in a HMP--based system. Instead of the holographic recording medium on the card, the information required to write the filter onto the SLM is stored on a card such as a smart card. The verifier reads this information from an inserted card and writes the prescribed correlation filter onto the SLM.

Encoded fingerprint filter information storage represents an enormous advance over the EMF in the collection, processing and distribution of fingerprint data. The enrolment procedure can now be an easily distributed operation.

Fingerprint scanners will simply digitize subscribers' fingerprints and relay the information to a filter-generating computer. The ease with which digital information can be transmitted makes the actual location of the computer irrelevant.

Moreover, advances in computer and communications technologies make the possibilities of a near real time enrolment a realistic possbility, With such a system a new subscriber would insert his newly issued blank card into the enrolment device, apply his fingerprints to the screen, and remove the initialized card several seconds later, thus completing the enrolment. The use of two or more fingerprints (a cluster) offers significant advantages over the use of just a single digit. Two approaches are possible.The first involves the digitization of the cluster as a single image, from which a filter is generated just as it would be generated for a single digit. (Digitization and filter generation are independent of the image content.) There is obviously more identifying information in a cluster than in a single digit, resulting in a filter which has the same amount of information (the same number of data bits) but with more unique information content, This information now includes relative finger position (i.e. relative length and orientation) because of the spatial relationships between the features of one digit of the cluster with the all the features on the other digit(s).

A second approach to the use of a cluster is to digitize each finger independently. Independent filters could be generated for each finger in the cluster, or a single composite filter could be derived. The case of two or more independent filters clearly represents more information than a single filter At verificationr the cluster is applied to the input of the verification device which in this application uses one or more sources of light. The card, holding independent correlation filter data for each digit in the cluster, is inserted into the card reader as usual. The verification device then displays each filter sequentially, verifying the presence of each digit in the cluster. A unique feature of this approach is that the correlation peak location at the output is dependent on the actual location of the target digit on the input screen.

By tracking the correlation peak location for each filter, the cluster shape (i.e. the relative finger lengths and widths) can be reconstructed. This provides additional biometric information to the system which can be used to improve system performance beyond what would be possible with only a single digit.

Alternatively, a single composite filter can be constructed from the digitized images of each finger in the cluster. This will provide a single filter capable of correlating with each digit in the cluster, and also provide relative digit location in the input plane of the verification device.

Encoded filter data also provides a convenient format for information storage and retrieval. The verification technology then becomes applicable where ever a centrally accessible database of authorized subscribers is desirable. This tyw of security system would not require the subscriber to carry a filter card at all. For example, the verifier could access the subscriber's encoded fingerprint information from a central database by cross referencing with the user's P.I.N. entered on a keyboard The fingerprint of the user is then correlated using a filter written onto the SLM with the centrally stored pattern information If the database is small enough and the SLM fast enough, a match for an input fingerprint can be searched for by sequentially scanning through the database.This approach may be desirable for access to high security installations or systems, etc., where there are relatively few authorized personnel. Current LCTV devices have scan rates of 6 Hz., allowing a search through a thirty record database in half a second. The speed can be expected to improve with advances in technology.

A further advantage of the digital filter format is the flexibility it offers for upgrading and improving the system.

Improved filter designs are readily implemented by the filter generating computer Existing cards can be upgraded at the subscriber's | 5 convenience at any enrolment facility. Upgrading of SLM drivers and electronics in the verifiers can be tolerated because of the electronic nature of these devices. Advances in relevant technology can be exploited, yet backwards compatibility can be always be ensured through software.

It should be noted that the optical arrangement for the correlator 38 illustrated in figure 1 is by way of example only.

Other optical arrangements are known. In this regard, reference is made to figures 2a, 2b, and 2c which shows a few of the known alternate arrangements for an optical correlator with Pt indicating the input, P2 the correlation filter, and P3 the detector. It will be recognlsed-that figure 2h LLlustrates the optical arrangement for the correlator illustrated in figure t.

While it is preferred that the detector is placed at the output plane of the correlator such that it receives a display of a correlation signal, information as to the correlation of the input and reference fingerprints is available at the output of the filter while the signal remains in the Fourier transform domain. Thus, for example, with reference to figure 1, correlation information could be extracted from the verification device 20 if lens 34 of correlator 38 were dispensed with and detector 36 were positioned more closely to the output of the SLM 26, A second source of identifying biometric information which can be obtained by the verification device is the cluster shape, the relative lengths and widths of the fingers of the subscriber. These can be measured using either electromechanical transducers or optical scanning devices. This is particularly useful when clusters of two or more fingers are used as input to the~ verification device. The probability of cluster shape values correlating with the fingerprint pattern information a-e extremely remote, thus adding a higher level of security and confidence to the verification.

Data on cluster width and relative finger lengths is stored along with the fingerprint pattern information upon registration of the subscriber. on verification, this added data is correlated with the cluster information collected by the position sensing equipment at the fingerprint input screen. This secondary correlation information is then used by the verification algorithm to determine whether the card user is in fact the authorized user.

With reference to figure 1, position transducers 40 are placed on the fingerprint input of the verification device. When an individual places his or her fingers on the input screen, the transducers will be displaced according to the lengths and widths of the user's fingers. In the case of optical scanning or detection equipment, the lengths and widths of the fingers are determined without any mechanical displacements of sensors, but through the interruption or modulation of an optical signal which is projected onto the input finger cluster from an appropriate location.

Other modifications will be apparent to those skilled in the art and, therefore, the invention is defined in the claims.

Claims (14)

What is claimed is:

1. A fingerprint verification device comprising the following: - a source of light for providing an illuminating beam along a beam path; - input means located in the beam path including means to receive at least one fingerprint of an individual for modulating the beam with data from the at least one fingerprint to form an information beam; - optical Fourier transform means in the beam path for providing a Fourier transform of the information beam in a transform plane; - a spatial light modulator fixed in said transform plane; - a card reader for reading encoded data from a card reprcsenting a correlation filter to be written to said spatial light modulator; - means for receiving said encoded data from said card reader and for writing a correlation filter to said spatial light modulator in accordance with said encoded data;; - verification means in the beam path at the output of said spatial light modulator for sensing a correlation signal which is the transform of the product between a correlation filter written to said spatial light modulator and the Fourier transform of at least one fingerprint of an individuaL received at said input means.

2. The fingerprint verification device of claim 1 wherein said,-input means comprises an input screen for the reception of at least one finger of an individual.

3. The fingerprint verification device of claim 1 wherein said input means comprises means to receive a recording of at least one fingerprint of an individual.

4. The fingerprint verification device of claim 1 wherein said'optical Fourier transform means comprises a lens.

5. The fingerprint verification device of claim 1 wherein said optical Fourier transform means comprises a holographic optical element.

6. The fingerprint verification device of claim 4 or claim 5 wherein said verification means is positioned so that any Fourier transform signal at said spatial light modulator is retransformed at said verification means.

7. The fingerprint verification device of claim 6 wherein said verification means comprises a detector in said beam path and a processor responsive to the output of said detector.

8. : The fingerprint verification device of claim 7 wherein said means for writing a correlation filter to said spatial light modulator includes a processor responsive to the output of said card reader and operatively connected to the input of said spatial light modulator.

9. A fingerprint verification device comprising the following: - a source of light for providing an illuminating beam along a beam path; - input means located in the beam path including means to receive a recording of at least one fingerprint of an individual for modulating the beam with data from the recording of at least one fingerprint to form an information beam; - optical Fourier transform means in the beam path for providing a Fourier transform of the information beam in a transform plane; - a spatial light modulator fixed in said transform plane; - a card reader for reading encoded data from a card representing a correlation filter to be written to said spatial light modulator ;;- - means responsive to said card reader for receiving said encoded data and for writing a correlation filter to said spatial light modulator in accordance with said encoded data; - verification means in the beam path at the output of said spatial light modulator for sensing a correlation signal which is the transform of the product between a correlation filter written to said spatial light modulator and the Fourier transform of the recording of at least one fingerprint of an individual received at said input means.

10. k fingerprint verification system comprising the following: - a source of light for providing an illuminating beam along a beam path; - input means located in the beam path including means to receive at least one fingerprint of an individual for modulating the beam with data from the at least one fingerprint to form an information beam; - optical Fourier transform means in the beam path for providing a Fourier transform of the information beam in a transform plane; - a spatial light modulator fixed in said transform plane; - a card storing a correlation filter in encoded data form; - a card reader for reading encoded data from said card - means for receiving said encoded data from said card reader and for writing a correlation filter to said spatial light modulator in accordance with said encoded data;; - verification means in the beam path at the output of said spatial light modulator for sensing a correlation signal which is the transform of the product between a correlation filter written to said spatial light modulator and the Fourier transform of at least one fingerprint of an individual received at said input means.

Ii. The fingerprint verification device of claim 10 wherein said input means is for receiving at least two fingerprints of an individual and wherein said encoded data comprises a correlation filter which is the superposition of a separate correlation filter for each of said at least two fingerprints.

12. The fingerprint verification device of claim 10 wherein said input means is for receiving at least two fingerprints of an individual and wherein said encoded data comprises a correlation filter which is a single image of said at least two fingerprints.

13. A method of generating a correlation filter for a fingerprint verification device of the type having; - a source of light for providing an illuminating beam along a beam path; - input means located in the beam path including means to receive at least two fingerprints of an individual for modulating the beam with data from the at least two fingerprints to form an information beam; - optical Fourier transform means in the beam path for providing a Fourier transform of the information beam in a transform plane; - a spatial light modulator fixed in said transform plane; - a card reader for reading encoded data from a card representing a correlation filter to be written to said spatial light modulator;; - means for receiving said encoded data from said card reader and for writing a correlation filter to said spatial light modulator in accordance with saii encoded data; - verification means in the beam path at the output of said spatial light modulator for sensing a correlation signal which is :the transform of the product between a correlation filter written to said spatial light modulator and the Fourier transform of at least two fingerprints of an individual received at said input means, compr#ising the steps of: - forming a correlation filter from each of said at least two fingerprints of an individual which said input means is designed to receive; - superposing each said formed correlation filter to record a correlation filter.

14. A method of generating a correlation filter for a fingerprint verification device of the type having: - a source of light for providing an illuminating beam along a beam path; - input means located in the beam path including means to receive at least two fingerprints of an individual for modulating the beam with data from the at least two fingerprints to form an information beam; - optical Fourier transform means in the beam path for providing a Fourier transform of the information beam in a transform plane; - a spatial light modulator fixed in said transform plane; - a card reader for reading encoded data from a card representing a correlation filter to be written to said spatial light modulator; ; means for receiving said encoded data from said card reader and for writing a correlation filter to said spatial light modulator in accordance with said encoded data; - verification means in the beam path at the output of said spatial light modulator for sensing a correlation signal which is the transform of the product between a correlation filter written to said spatial light modulator and the Fourier transform of at least two fingerprints of an individual received at said input means, comprising the steps of: - recording a correlation filter from a cluster of all of said at least two fingerprints of an individual which said input means is designed to receive.