KR100607577B1 - Method and apparatus for distinguishing forged fingerprint for optical fingerprint acquisition apparatus - Google Patents

Abstract

In the present invention, in fingerprint recognition, a biometric fingerprint input by a living person's hand and an artificial fingerprint (fake fingerprint) imitating the same can be identified using an absorption fingerprint acquisition device and a scattering fingerprint acquisition device. A method and apparatus are disclosed. The method according to the present invention comprises the steps of: (1) acquiring a first image by an optical scattering method (or absorption method) on a fingerprint input window to which a fingerprint to be acquired is contacted; (2) a contact body placed on the fingerprint input window. Acquiring a second image by an optical absorption method (or scattering method) with respect to (3) comparing the first and second images, and when the two images are inverted from each other, And determining that the contact is a fake fingerprint when both images are not inverted.

Fingerprint, fake fingerprint, bio fingerprint, film, absorption method, scattering method, fingerprint image

Description

Method and apparatus for distinguishing fingerprints of optical fingerprint acquisition device {Method and apparatus for distinguishing forged fingerprint for optical fingerprint acquisition apparatus}

1 is a block diagram of a general absorption type fingerprint acquisition device.

2 is a view for explaining the operation of the absorption type fingerprint acquisition device for the bio fingerprint.

3 is a block diagram of a general scattering fingerprint acquisition device.

4 is a view for explaining the operation of the scattering fingerprint acquisition device for the bio fingerprint.

5 is a bio fingerprint image obtained by the absorption method and the scattering method, respectively.

6 is a view for explaining the operation of the absorption method and scattering fingerprint acquisition device for the imitation fingerprint.

7 is an imitation fingerprint image acquired by the absorption method and the scattering method, respectively.

8 is a block diagram of an imitation fingerprint identification apparatus according to the present invention.
9 is a view for explaining a problem in the mounting structure of the imitation fingerprint identification apparatus according to the present invention.
FIG. 10 is a diagram for explaining the problem solved in the case of FIG.

In the present invention, in fingerprint recognition, a biometric fingerprint input by a living person's hand and an artificial fingerprint (fake fingerprint) imitating the same can be identified using an absorption fingerprint acquisition device and a scattering fingerprint acquisition device. A method and apparatus are disclosed.

As fingerprint recognition devices are widely used in personal authentication fields such as access authentication and payment, security enhancement is required. Although many fingerprint recognition algorithms and algorithms for coping with fake fingerprints are being developed one after another to enhance the accuracy of fingerprint recognition, fingerprint replication technology is also developing accordingly.

There are several prior patents regarding the method of identifying the duplicated fingerprints. 1) Japanese Unexamined Patent Application Publication No. 11-45338 discloses a technique for detecting a fake fingerprint by detecting a biopotential generated in a living body, but the electrode for detecting potential in a state in which the fake fingerprint is in contact with a fingerprint input window. However, in case of contact with the living body, the imitation fingerprint cannot be recognized, and additional hardware and arithmetic processing part must be provided because the detection signal processing and frequency analysis process are separately required. 2) Pupil Publication (Pyeong) 10-290796 discloses a method for identifying a fake fingerprint by measuring various forms of stimuli to a living body and responding to the stimulus. However, the method itself for analyzing the response of the human body by external stimulation is not only artificially unpleasant to the user, but also difficult to quantify the response form to the stimulus regularly. 3) Pupil Publication No. 9-259272 discloses a method for identifying a fake fingerprint by detecting the presence and number of sweat glands in a fingerprint image. According to the current imitation fingerprint manufacturing technology, not only the fingerprint form but also the glands can be reproduced as it is not realistic. 4) Publication No. 7-308308 discloses a technique for identifying fake fingerprints by detecting changes in oxygen concentration and blood flow using a quantity of light transmitted by irradiating a specific light beam. However, when the imitation fingerprint is made of a material that transmits well with respect to the frequency of the light source emitted from the light source element and is worn on the finger, there is a limitation that the imitation fingerprint cannot be identified. 5) In addition, a technique for identifying a fake fingerprint by a method of recognizing a pulse of a fingertip by using a pressure sensor has been developed, but in this case, there is a limitation in that it cannot cope with other input information similar to a pulse.

In addition to the above limitations, in recent years, the technology for manufacturing thin imitation fingerprints made of materials such as silicone or film has been developed, so that the possibility of distinguishing the biological fingerprint from the imitation fingerprints by any of the above methods is extremely high when worn directly on the living body. It becomes thin. In particular, even in the case of a fingerprint printed on an OHP film or the like, it is difficult to select a fake fingerprint.

The present invention is to accurately identify the fingerprint printed on the film difficult to solve the existing imitation fingerprint identification method, in the case of the bio fingerprint is the result image of the scattering fingerprint acquisition device and absorption fingerprint acquisition device is inverted and output However, the fingerprint printed on the film (hereinafter, simply referred to as "fake fingerprint") was developed based on the fact that the fingerprint acquisition device obtains the same result image regardless of the scattering method or the absorption method.

An object of the present invention is to provide a method and apparatus for operating a fingerprint acquisition device by applying both a scattering method and an absorption method using such characteristics, and determining whether the fingerprint is a biometric fingerprint or a fake fingerprint by comparing images acquired by each method. .

Typical optical fingerprint input devices include absorption methods and scattering methods. 1 is a principle diagram of an absorption type fingerprint input device, and includes a light source 112, a prism 110, a lens unit 114, an image sensor 116, and an image processing unit 125. The oblique surface of the prism 110 is a fingerprint input window 118 to which the fingerprint to be acquired is in contact, and the inner surface of the fingerprint input window 118 is a total reflection surface causing total reflection.

With no fingerprint applied to the fingerprint input window 118, the light from the light source 112 is totally reflected on the inner surface of the fingerprint input window 118 of the prism 110 to the image sensor 116 through the lens 114. Incident. When the fingerprint is placed on the fingerprint input window 118, the incident light 127 is totally reflected on the inner surface of the fingerprint input window 118 because the valley 130 of the fingerprint is separated from the fingerprint input window 118 as shown in FIG. 2. Since the light reaches the image sensor 116 as the reflected light 128 and the ridge of the fingerprint is in contact with the fingerprint input window 118, most of the incident light 127 'is absorbed by the ridge without total reflection on the inner surface. Only the reflected light 129 reaches the image sensor 116.

Therefore, the amount of light incident on the image sensor 116 is different depending on the valleys and ridges of the fingerprint, and eventually the image sensor 116 outputs different levels of electrical signals according to the pattern of the fingerprint. The image processor 125 recognizes the fingerprint pattern by shaping the output value of the image sensor 116 into a digital signal and processing the image.

3 shows a principle diagram of a scattering fingerprint acquisition device. The configuration includes a light source 312, a prism 310, a lens unit 314, and an image sensor 316 similar to the case of FIG. 1, but unlike the absorption method of FIG. 1, light is emitted from the light source 312. Instead of total internal reflection because the incident light enters the fingerprint input window 318 of the prism 310 at a right angle or a much smaller angle than the critical angle, the incident light 327 is incident on the valley of the fingerprint that is not in contact with the fingerprint input window 318. Passing through the input window 318 and not reaching the image sensor, the incident light 327 'is scattered on the ridge surface of the fingerprint and scattered light 329 is detected by the image sensor 316 through the lens unit 314. (See Fig. 4).

As described above, in the absorption type fingerprint acquisition device, since absorption of light occurs in the ridge portion, the fingerprint image formed on the image sensor has dark ridges and bright bones. On the other hand, in the scattering fingerprint acquisition device, light scattering occurs in the ridge, so that the fingerprint image formed on the image sensor has bright ridges and dark valleys, resulting in the absorption image and the reversed fingerprint image. In FIG. 5, the inverted state of the fingerprint image can be confirmed. FIG. 5A illustrates a biofingerprint image acquired by the scattering fingerprint acquisition apparatus, and FIG. 5B illustrates a biofingerprint image acquired by the absorption fingerprint acquisition apparatus.

On the other hand, in the case of the imitation fingerprint printed on the film, the acquired image is obtained in the same manner without being inverted from each other, whether it is an absorption method or a scattering method. This can be seen from FIG. 6. In the case of the imitation fingerprint 400 of the type printed on the film as shown in Figure 6 in the dark portion (mainly black) covered with the absorbent material, the absorption method (Fig. 6 (a)) or scattering method ( b)), regardless of whether the light is absorbed and appears dark, and in the bright areas (mainly the substrate), the light appears to be bright. Therefore, in the case of imitation paper of the form printed on the film, the image of the same form is acquired whether the absorption method or scattering method. Fig. 7 illustrates an image obtained from the imitation fingerprint 400 in the form printed on the film. Fig. 7A is an image acquired by the absorption type fingerprint acquisition device, and (b) illustrates an image acquired by the scattering mode fingerprint acquisition device. It can be seen that there is no inversion of the image compared with FIG. 5.

In this way, since the images obtained from the biometric fingerprint and the fake fingerprint using both the absorption method and the scattering fingerprint acquisition device are different from each other, using this property can completely identify the imitation fingerprints printed on the film as in the method of the present invention. It becomes possible.

In other words, the method for determining the imitation fingerprint according to the present invention is a method for determining whether a contact is a biometric fingerprint or an imitation fingerprint by acquiring an image of an object (hereinafter, referred to as a "contact body") in contact with the fingerprint input window. Acquiring a first image by an optical absorption method (or scattering method) for a contact placed in the input window; (2) optically scattering (or absorption method) method for the contact placed in the fingerprint input window. Acquiring a second image, (3) comparing the first and second images, and in the case where both images are inverted with each other, determining that the contact is a biofingerprint, and the two images are not inverted. In the case of a state comprising the step of determining that the contact is a fake fingerprint. Here, the meanings in the parenthesis are intended to indicate that the order of application of the absorption method and the scattering method in the present invention is optional and can be interchanged.

In the determination of the imitation fingerprint in the step (3), the sum of the differences of the gray values in the predetermined region of each acquired image is calculated, and when the sum of the differences between the gray values of both is larger than the reference value, the bioprint is read out. When the sum of the differences of the gray values in the area is smaller than the reference value, a method of reading with a dummy fingerprint can be adopted.

In more detail, the sum of the differences of gray values may be obtained by the equation illustrated in Equation 1. That is, the difference of gray values for pixels corresponding to the same position in a predetermined area is obtained, and the sum of differences of gray values for all pixels in the predetermined area is obtained.

G _a (a, b): Gray value at coordinates (a, b) in an image acquired by absorption

G _s (a, b): Gray value at coordinates (a, b) in an image acquired by scattering

j, k: starting coordinates of the predetermined area

(m + 1) x (n + 1): the size of the predetermined area

Hereinafter, an embodiment of the apparatus for identifying a fingerprint according to the present invention will be described with reference to the drawings.

The difference between the absorption method and the scattering fingerprint acquisition device as described above is different depending on whether the incident light is incident on the fingerprint input window at an angle causing total internal reflection. Therefore, in order to implement this as one optical system, as shown in FIG. 8, two light sources 20 and 30 are installed in one prism 10 to simultaneously implement an absorption method and a scattering method.

In more detail with reference to Figure 8, the fingerprint acquisition device according to the present invention

A prism 10 including a fingerprint input window 12 to which a fingerprint to be acquired is contacted and a fingerprint exit surface 14 to which a fingerprint image is outputted;

A first light source 20 installed at a position that emits light 22 at an angle totally reflected from the fingerprint input window 12 of the prism 10,

A second light source 30 installed at a position that emits light 32 at an angle that is not totally reflected from the fingerprint input window 12 of the prism 10,

A light source switching unit 40 for sequentially operating the first light source 20 and the second light source 30,

A focusing lens 50 for focusing the first image and the second image emitted from the fingerprint output surface 14 of the prism 10 when the first light source 20 is turned on and the second light source 30 is turned on; Image sensor 60 for detecting an image,

When the first image signal and the second image signal detected by the image sensor 60 have a value in which the bone and the ridge of both images are inverted, it is determined to be a bio fingerprint, and the bone and the ridge of both images are determined. When the value of the non-inverted state is included, the image comparator 70 determines to be a fake fingerprint.

Prism 10 may use a triangular prism, but need not necessarily be a triangle. Conventionally, parallelograms or trapezoidal prisms are also used.

The first light source 20 is for implementing an absorption type fingerprint acquisition device, and is installed at a position where the light input 22 is irradiated to the fingerprint input window 12 but can be totally reflected. This position will vary depending on the shape of the prism 10 or the refractive index of the medium.

The second light source 30 is to implement a scattering fingerprint acquisition device, and is installed at a position where the maximum scattering effect can be obtained without being totally reflected in the fingerprint input window 12. The position of the first light source 20 and the second light source 30 can be easily designed from the existing fingerprint acquisition device.

The light source switching unit 40 is for sequentially turning on the first light source 20 and the second light source 30. When two light sources are turned on at the same time, since the fingerprint acquisition device of the present invention does not operate properly, each light source is sequentially turned on to acquire an image in sequence.

Since the focusing lens 50 and the image sensor 60 are essential components in the optical fingerprint image acquisition device, a separate description thereof will be omitted.

In the image comparing unit 70, an image acquired when the first light source 20 is turned on (that is, an image acquired by the absorption method) and an image acquired when the second light source 30 is turned on (that is, by the scattering method). The acquired images) are compared to read whether or not the two images are inverted with each other.

The reading method by comparing the images can be arbitrarily implemented by those skilled in the art of image processing or graphics processing. As an example, the sum of differences of gray values in a predetermined area of each acquired image is calculated. If each image is inverted, the sum of the difference between the gray values of the two will be very large. On the contrary, if the image is not inverted and is the same, the sum of the differences of the gray values in the predetermined area will be almost the same (there may be some differences due to noise, but the difference due to noise is sufficiently detected by known image processing techniques. Available). In addition, it is possible to read the inversion of both images by various techniques at the discretion of those skilled in the art.

The image comparator 70 may read a fake fingerprint to stop the further fingerprint authentication procedure in the case of the fake fingerprint, and in the case of the bio fingerprint, the fingerprint feature data extraction and the fingerprint authentication procedure may be included. .

Meanwhile, in the fingerprint acquisition device according to the present invention, since two light sources 20 and 30 are used as shown in FIG. 8, the following problem may occur in the mounting structure of the device. For example, in the case of a device adopting a mounting structure as shown in FIG. 9, a prism 904 is embedded in a space enclosed by the housing 902 and a scattering light source (not shown) and an absorption method are provided outside the housing 902. The dragon light source 908 is installed at an appropriate position. In the case of FIG. 8, since the absorption type light source 908 should be installed on the opposite surface of the fingerprint contact surface 905, the light transmission hole 910 for entering the absorption type light source 908 into the prism 904. It must be formed in the housing 902. However, in such a mounting structure, when the image of the contact body is acquired by the scattering method, a problem may occur such that the light of the scattering light source is reflected back into the prism through the light transmitting hole 910. Such light is likely to act as noise for optics that are precisely designed with sophisticated optical parameters. In order to solve this problem, in the fingerprint acquisition device according to the present invention, it is preferable to provide an anti-reflective scattering film 920 in the hole 910 through which the absorption type light source 908 enters the prism 904 (see FIG. 10). ). The anti-reflective scattering film 920 does not reflect light from the inside of the prism 904 and light of the absorption type light source 908 is scattered to enter the prism 904.

Although a preferred embodiment of the present invention has been described above with reference to the drawings, the method and apparatus for identifying a fingerprint according to the present invention includes the concept of using both an absorption method and a scattering fingerprint acquisition device. It is not intended to be limited to the examples, but will be determined by the appended claims.

1) According to the present invention, it is also possible to identify the imitation fingerprints in the form printed on the film, which cannot be discriminated by the conventional method.

2) The additional configuration of hardware and software is less than the effect.

3) The fake fingerprint discrimination algorithm is simple. Since the fake fingerprint can be identified only by comparing the first image and the second image, there is no software overhead.

4) High security. There is no additional equipment, and only one light source is added, and if it is hidden so that it cannot be seen from the outside, it is difficult for the user to know the existence and operation of the fake fingerprint identification device.

5) In addition, in the case of the optical fingerprint input device, residual fingerprints remain due to sebum or contaminants according to the contact of the fingerprint. At this time, if light is incident from the external light source at a specific range of angles instead of the internal light source, it remains in the image sensor. Fingerprints can be detected. When the residual fingerprint is detected by the image sensor, the fingerprint recognition device may mistake the residual fingerprint as the actual biometric fingerprint. According to the present invention, the problem of mistaken for such a residual fingerprint is also solved. This is because the remaining fingerprint on the fingerprint input window acts like a fake fingerprint printed on the film.

Claims (8)

A method of determining whether a contact is a biometric fingerprint or an imitation fingerprint by acquiring an image of an object (hereinafter referred to as "contact body") in contact with the fingerprint input window, (1) acquiring a first image of the contact body placed in the fingerprint input window by optical absorption; (2) acquiring a second image by an optical scattering method for the contact placed on the fingerprint input window; (3) comparing the first and second images and determining that the contact is a bio fingerprint if both images are inverted from each other, and imitating the contact if both images are not inverted. Imitation fingerprint determination method comprising the step of determining that the door. A method of determining whether a contact is a biometric fingerprint or an imitation fingerprint by acquiring an image of an object (hereinafter referred to as "contact body") in contact with the fingerprint input window, (1) acquiring a first image by an optical scattering method for a contact placed on the fingerprint input window; (2) acquiring a second image by an optical absorption method for the contact placed on the fingerprint input window; (3) The first and second images are compared to determine that the contact is a bio fingerprint if both images are inverted from each other, and if the two images are not inverted, the contact is faked. Imitation fingerprint determination method comprising the step of determining that the door. The method according to claim 1 or 2, wherein in step (3), the sum of differences of gray values in a predetermined region of each acquired image is calculated, and when the sum of the differences of the gray values of both is larger than the reference value, the bioprint is read. And when the sum of the differences of the gray values in the predetermined area is smaller than the reference value, the imitation fingerprint reading method. An apparatus for acquiring an image of an object in contact with a fingerprint input window (hereinafter referred to as "contact body") to determine whether the contact body is a fingerprint or a fake fingerprint, A prism including a fingerprint input window and a fingerprint exit surface on which an image of the input fingerprint is output; A first light source installed at a position to emit light at an angle totally reflected from the fingerprint input window of the prism, A second light source installed at a position that emits light at an angle that is not totally reflected from the fingerprint input window of the prism, A light source switching unit which sequentially operates the first light source and the second light source, An image sensor detecting a first image emitted from the fingerprint exit surface of the prism when the first light source is turned on and detecting a second image exiting from the fingerprint exit surface of the prism when the second light source is turned on; When the first image and the second image detected by the image sensor are processed to determine that both images have a value inverted with each other, it is determined that the fingerprint is biometric, and when both images have values that are not inverted with each other Imitation fingerprint discrimination apparatus including an image comparison unit that is determined to be a fake fingerprint. The apparatus of claim 4, wherein the prism is a triangular prism. The apparatus of claim 4, wherein the first light source constitutes an optical system of an absorption type fingerprint acquisition device, and the second light source constitutes an optical system of a scattering type fingerprint acquisition device. The apparatus of claim 4, wherein the image comparator Means for calculating a sum of differences of gray values in a predetermined region of each acquired image; And a means for reading the biometric fingerprint when the sum of the differences between the gray values is greater than the reference value, and reading the dummy fingerprint when the sum of the differences of the gray values in the predetermined area is smaller than the reference value. Device. 5. The method of claim 4, wherein an anti-reflective scattering film is disposed on a path through which the first light source enters into the prism, so that light from the prism is not reflected and light of the first light source is scattered to enter the prism. Imitation fingerprint discrimination apparatus.

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