Patent Publication Number: US-2010115597-A1

Title: Computer readable medium, image processing system, and image processing device

Description:
This application is based on the application No. 2008-284318 filed in Japan, the contents of which are hereby incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a technique of registering reference data on the basis of which authentication is executed in the biometric authentication technology using biometric information. The present invention more specifically relates to a computer readable medium, and an image processing system and an image processing device with a biometric authentication function. 
     2. Description of the Background Art 
     Image processing devices called as complex devices or MFPs (multifunction peripherals) include such a device that executes user authentication when used by a user. The user authentication in the image processing device is intended to raise the security level of the device itself, to limit users who are authorized to use a costly function such as color copy, or to achieve other objects. So, when a user performs an operation for authentication and is successfully authenticated, the user is put in the state of being logged into the image processing device. As a result, the user is allowed to use a function for which the user has been authorized in advance. 
     In order to execute user authentication with a higher security level, an image processing device executing biometric authentication by reading biometric information such as the fingerprint or the finger vein pattern of a user is recently coming into widespread use. According to the biometric authentication technology of this type, biometric information applied as reference data to be used in user authentication is registered in advance. Then, biometric information read from a user&#39;s living body is checked against the reference data in the user authentication, thereby authenticating the user. 
     In order to register reference data to be used in biometric authentication, biometric information is read several times, optimum biometric information is selected from the several pieces of biometric information, and the selected optimum biometric information is registered as reference data. This known technique is introduced for example in Japanese Patent Application Laid-Open No. 2007-648. In this technique, if a finger is held over a biometric information reader without changing its posture, several readings do not achieve any effect. As a result, appropriate reference data cannot be registered. In response, according to the disclosure of Japanese Patent Application Laid-Open No. 2007-648, it is determined whether or not a user&#39;s finger has taken off the biometric information reader after each reading when biometric information is read several times. If the user&#39;s finger is not taken off the biometric information reader, the user is prompted to take the finger off the biometric information reader. 
     In the biometric authentication technology described above, authentication of a user may end in failure even when the user is a rightful user whose reference data is registered. In order to avoid this false authentication, more appropriate biometric information should be selected for registering reference data. Like in the above-described conventional technique, biometric information is read several times, optimum biometric information is selected from the several pieces of biometric information, and the selected optimum biometric information is registered as reference data. In this case, by increasing the number of times biometric information is read, more appropriate biometric information can be selected as reference data. That is, after a user performs an operation for reading biometric information several times, features quantities of the biometric information obtained by a biometric information reader differ among the readings. However, when the biometric information is read from the same user, feature quantities of the biometric information are generally found within a certain range of a feature distribution. As a number of times of reading increases, biometric information found at a closer position to the center in the feature distribution can be selected. So, by applying the selected biometric information as reference data, the incidence of false authentication is reduced. 
     However, indefinitely increasing the number of times of reading of biometric information for registering reference data considerably deteriorates operability in the registration of reference data, and generates enormous volumes of data to be referred to in calculation for selecting optimum reference data. So, considerably a lot of time for processing is required. Therefore, from a practical point of view, the number of times of reading of biometric information for registering reference data should be limited to a certain number. Like in the above-described conventional technique, when biometric information is read several times, optimum biometric information is selected from the several pieces of biometric information, and the selected optimum biometric information is registered as it is as reference data, it cannot be confirmed whether or not the selected biometric information is appropriate information. So, if false authentication occurs frequently in actual biometric authentication performed after the reference data is registered, reference data should be registered again. 
     SUMMARY OF THE INVENTION 
     The present invention is intended to solve the problems described above. Thus, the present invention is intended to provide a computer readable medium, an image processing system, and an image processing device capable of determining in advance whether or not biometric information selected as reference data is optimum information, and capable of optimizing reference data when the reference data to be used in biometric authentication is registered, thereby reducing the incidence of false authentication in actual biometric authentication. 
     First, the present invention is directed to a computer readable medium on which a program is stored. The program being executed by a computer to which a biometric information reader for performing biometric authentication is connected. The program causes the computer to operate as a system comprising: a biometric information acquisition part for acquiring N pieces of biometric information by causing the biometric information reader to read biometric information N times (N is an integer of 3 or greater); a reference data selection part for selecting one piece of biometric information from the N pieces of biometric information acquired by the biometric information acquisition part, and for provisionally setting the selected biometric information as reference data to be used in biometric authentication; an authentication test execution part for acquiring authentication-testing biometric information by causing the biometric information reader to read biometric information once, and for executing an authentication test by checking the authentication-testing biometric information against the reference data; and a reference data optimization part for selecting one piece of biometric information from (N+1) pieces of biometric information including the N pieces of biometric information acquired by the biometric information acquisition part and the authentication-testing biometric information acquired by the authentication test execution part, thereby optimizing the reference data. 
     Second, the present invention is directed to an image processing system comprising an image processing device with a biometric authentication function, and an information processing device for generating reference data to be used in biometric authentication in the image processing device and for registering the reference data in the image processing device. The image processing device and the information processing device are connected through a network. In this image processing system, the information processing device includes: a biometric information reader for reading biometric information; a biometric information acquisition part for acquiring N pieces of biometric information by causing the biometric information reader to read biometric information N times (N is an integer of 3 or greater); a reference data selection part for selecting one piece of biometric information from the N pieces of biometric information acquired by the biometric information acquisition part, and for provisionally setting the selected biometric information as reference data to be used in biometric authentication; an authentication test execution part for acquiring authentication-testing biometric information by causing the biometric information reader to read biometric information once, and for executing an authentication test by checking the authentication-testing biometric information against the reference data; a reference data optimization part for selecting one piece of biometric information from (N+1) pieces of biometric information including the N pieces of biometric information acquired by the biometric information acquisition part and the authentication-testing biometric information acquired by the authentication test execution part, thereby optimizing the reference data; and a reference data transmission part for transmitting the reference data optimized by the reference data optimization part to the image processing device. Further, the image processing device includes: a biometric information reader for reading biometric information; a recording part for recording therein the reference data received from the information processing device; and an authentication processor for executing biometric authentication by checking biometric information received from the biometric information reader of the image processing device against the reference data recorded in the recording part, and for enabling a function relating to image processing when biometric authentication ends in success. 
     Third, the present invention is directed to an image processing device with a biometric information reader, the image processing device performing biometric authentication by comparing biometric information received from the biometric information reader and reference data registered therein in advance, and enabling a function relating to image processing when the biometric authentication ends in success. The image processing device comprises: a biometric information acquisition part for acquiring N pieces of biometric information by causing the biometric information reader to read biometric information N times (N is an integer of 3 or greater); a reference data selection part for selecting one piece of biometric information from the N pieces of biometric information acquired by the biometric information acquisition part, and for provisionally setting the selected biometric information as reference data to be used in biometric authentication; an authentication test execution part for acquiring authentication-testing biometric information by causing the biometric information reader to read biometric information once, and for executing an authentication test by checking the authentication-testing biometric information against the reference data; a reference data optimization part for selecting one piece of biometric information from (N+1) pieces of biometric information including the N pieces of biometric information acquired by the biometric information acquisition part and the authentication-testing biometric information acquired by the authentication test execution part, thereby optimizing the reference data; and a reference data registration part for registering the reference data optimized by the reference data optimization part. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an exemplary configuration of an image processing system; 
         FIG. 2  is a block diagram showing the hardware configuration of the image processing system; 
         FIGS. 3A and 3B  show exemplary structures of a biometric information reader; 
         FIG. 4  is a block diagram explaining functions realized in an information processing device; 
         FIGS. 5A and 5B  conceptually show the processing executed by a reference data selection part when the distribution of the feature quantities of three pieces of biometric information is represented two-dimensionally; 
         FIG. 6  conceptually shows the processing executed by an authentication test execution part when a feature distribution is represented two-dimensionally; 
         FIGS. 7A and 7B  conceptually show the processing performed by a reference data optimization part when the distribution of the feature quantities of four pieces of biometric information is represented two-dimensionally; 
         FIGS. 8 and 9  are flow diagrams explaining an exemplary process sequence executed in the information processing device based on a program; 
         FIG. 10  is a flow diagram explaining in detail the process sequence of reference data optimization; 
         FIGS. 11A and 11B ,  FIGS. 12A and 12B , and  FIGS. 13A and 13B  show examples of screens displayed on a display unit during the course of the process in the information processing device; 
         FIG. 14  is a block diagram showing the configuration of functions in an image processing device according to a first preferred embodiment of the present invention; and 
         FIG. 15  is a block diagram showing the configuration of functions in an image processing device according to a second preferred embodiment of the present invention. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Preferred embodiments of the present invention are described in detail below with reference to figures. In the description given below, those elements which are shared in common among the preferred embodiments are represented by the same reference numerals, and these elements are not discussed repeatedly for the same description. 
     First Preferred Embodiment 
       FIG. 1  shows an exemplary configuration of an image processing system  1  to which the present invention is applied. The image processing system  1  comprises an information processing device  2  constituted by a generally-used computer, and an image processing device  3  for executing a job relating to image processing. The information processing device  2  and the image processing device  3  are connected to each other through a network  4  such as LAN (Local Area Network), so that data communication between the information processing device  2  and the image processing device  3  is enabled. 
     The image processing device  3  is also called as an MFP (multifunction peripheral) having several functions relating to image processing such as those of a copier, a scanner, a FAX, a printer, and others. The image processing device  3  includes a scanner unit  31  set at the upper part of the device body for reading the image of a document. An operation panel  34  is set on the front side of the scanner unit  31 , and which is operated by a user when the user gives instructions of job execution, etc. A printer unit  32  responsible for print output is set in the central part of the device body. A sheet feed unit  33  is set under the printer unit  32 , and which keeps a stock of printing sheets and feeds sheets to the printer unit  32  when the printer unit  32  executes print output. The image processing device  3  puts each of the scanner unit  31 , the printer unit  32 , the sheet feed unit  33  and others into operation to execute a job relating to image processing. The image processing device  3  can also be connected to a telephone line not shown in  FIG. 1 , by which the image processing device  3  can transmit and receive facsimile data, for instance. 
     The image processing device  3  of the first preferred embodiment is so configured as to execute biometric authentication (user authentication) before a user starts using the image processing device  3 . For this purpose, the image processing device  3  includes a working table  35  on a lateral side of the device body. A biometric information reader  9  ( 9   b ) is set on the working table  35 . The biometric information reader  9   b  may be set at an alternative position, for example at the operation panel  34 . The biometric information reader  9   b  reads a finger vein pattern as biometric information of a user who tries to use the images processing device  3 . Biometric information read by the biometric information reader  9   b  is output to the device body of the image processing device  3 , and thereafter the image processing device  3  executes biometric authentication (user authentication). 
     The image processing device  3  holds reference data BD which is registered for each user therein in advance to be used in biometric authentication. The image processing device  3  checks biometric information input from the biometric information reader  9   b  against the reference data BD registered therein in advance to execute biometric authentication. If authentication ends successfully, the image processing device  3  enables a function relating to image processing for which a user has been authorized in advance from the several functions described above such as those of a copier, a scanner, a FAX, a printer, and others. As a result, the user is allowed to use the function. If the authentication ends in failure, the image processing device  3  does not enable a function relating to image processing. So, the user is still not allowed to use a function which is imposed restriction of use in the image processing device  3 . 
     The information processing device  2  is so configured as to generate the reference data BD to be registered in advance in the image processing device  3 , and to transmit the generated reference data BD through the network  4  to the image processing device  3 . The information processing device  2  is constituted by additionally connecting a biometric information reader  9  ( 9   a ) to a generally-used computer including a computer main unit  20 , a display unit  21  such as a CRT (cathode ray tube) or an LCD (liquid crystal display), and a manipulation input unit  24  with a keyboard  22  and a mouse  23 . The biometric information reader  9   a  is the same type of device as the biometric information reader  9   b  of the image processing device  3  for reading the finger vein pattern of a user as biometric information. In order to register a user trying to use the image processing device  3  with the information processing device  2 , the biometric information reader  9   a  reads biometric information from the finger of the user, and outputs the read biometric information to the information processing device  2 . Then, the information processing device  2  generates the reference data BD to be used in biometric authentication in the image processing device  3  based on the biometric information input from the biometric information reader  9   a , and transmits the generated reference data BD to the image processing device  3 . 
     The image processing device  3  stores therein the reference data BD received from the information processing device  2 , and refers to the reference data BD at the time of biometric authentication. So, in a first preferred embodiment of the present invention, the information processing device  2  generates the reference data BD registered for each user in advance in the image processing device  3 . 
       FIG. 2  is a block diagram showing the hardware configuration of the image processing system  1  of the first preferred embodiment. As shown in  FIG. 2 , the image processing device  3  includes the operation panel  34 , the scanner unit  31 , the printer unit  32 , the sheet feed unit  33 , an image processing unit  36 , a communication processing unit  37 , a hard disk drive  38 , a controller  40 , a network interface  44 , a storage unit  45 , and an input/output interface  47  that are connected to each other to allow data communication between these parts through a data bus  49 . The biometric information reader  9   b  is connected to the input/output interface  47 . 
     The controller  40  controls the operation of the image processing device  3  as a whole. The controller  40  includes a CPU  41 , a RAM  42 , and a ROM  43 . The CPU  41  reads a program stored in the hard disk drive  38  and executes the program, thereby realizing each function of the controller  40 . The controller  40  stores the reference data BD received from the information processing device  2  through the network interface  44  into the storage unit  45  constituted by a nonvolatile memory or the like. At the time of biometric authentication, the controller  40  inputs the biometric information of a user from the biometric information user  9   b  and retrieves the reference data BD from the storage unit  45 , thereby executing authentication. If a user is successfully authenticated, the controller  40  enables at least one function for which the authenticated user has been authorized in advance, and controls each of the operation panel  34 , the scanner unit  31 , the printer unit  32 , the sheet feed unit  33 , the image processing unit  36  and the communication processing unit  37 , thereby executing a job specified by the user. The image processing unit  36  is responsible for calculation required for executing a job such as scaling of an image, format conversion of image data and the like. The communication processing unit  37  comes into operation when transmitting and receiving facsimile data, for example. 
     The information processing device  2  includes a CPU  11 , a RAM  12 , a ROM  13 , a network interface  14 , input/output interfaces  15 ,  16  and  19 , and a hard disk drive  17  that are connected to each other to allow data communication between these parts through a data bus  29 . The network interface  14  is for connecting the information processing device  2  to the network  4 . The input/output interfaces  15 ,  16  and  19  are connected to the display unit  21 , the manipulation input unit  24 , and the biometric information reader  9   a  respectively. An application program  18  for generating reference data to be used in biometric authentication is installed in advance in the hard disk drive  17 . The CPU  11  reads and executes the program  18 , so that the CPU  11  realizes each function described later to generate reference data BD to be transmitted to the image processing device  3 . The RAM  12  temporarily holds various types of data generated while the CPU  11  executes processing based on the program  18 . The ROM  13  holds data and so on stored in advance therein that is required for the CPU  11  to execute processing based on the program  18 . 
       FIGS. 3A and 3B  show exemplary structures of the biometric information reader  9  ( 9   a ,  9   b ) of the first preferred embodiment.  FIG. 3A  is a perspective view, and  FIG. 3B  is a sectional view during the use of the biometric information reader  9 . As shown in  FIG. 3A , the biometric information reader  9  has a recess  92  set at the central part of the front side of the main unit  91  as a base for a user to insert his or her finger into and place over. A pair of support walls  93  set on the right and left sides of the main unit  91  hold a top board  94  at a certain position above the main unit  91 . As shown in  FIG. 3B , the top board  94  is given a lighting unit  96  with at least one light source  95  for illuminating a finger F inserted into the recess  92  of the main unit  91  from above. The main unit  91  is given an image capturing unit  97  set lower of the internal side of the recess  92 . The image capturing unit  97  receives light passing through the finger F to capture the image of a vein pattern VP of the finger F. The image captured by the image capturing unit  97  is used as biometric information. The biometric information reader  9  of the first preferred embodiment has the top board  94  set above the main unit  91  to shield environmental light such as room lighting. So, the image of the vein pattern VP is able to be captured under the condition of less affected by the environmental light when the image capturing unit  97  captures the image of the vein pattern VP. Thus, an image with a high degree of reliability can be obtained. 
       FIG. 4  is a block diagram showing each function realized by execution of the program  18  by the CPU  11  in the information processing device  2 . More specifically, in order for the information processing device  2  to generate reference data to be transmitted to the image processing device  3 , the CPU  11  becomes operative to function as a biometric information acquisition part  51 , a reference data selection part  52 , an authentication test execution part  53 , a reference data optimization part  54 , and a reference data transmission part  55 . The RAM  12  contains a biometric information storage area  61  into which biometric information input from the biometric information reader  9   a  is stored. The biometric information storage area  61  has a sample storage area  62  and an authentication-testing storage area  63 . Each part of the information processing device  2  is described next. 
     The biometric information acquisition part  51  causes the biometric information reader  9   a  to read biometric information N times (N is an integer of 3 or greater) to acquire N pieces of biometric information. By outputting a command to the biometric information reader  9   a  to start reading, the biometric information acquisition part  51  causes the biometric information reader  9   a  to read biometric information (capture the image of the vein pattern VP). After outputting the command, the biometric information acquisition part  51  inputs biometric information obtained by reading the finger vein pattern of a user from the biometric information reader  9   a , and stores the input biometric information into the sample storage area  62  in the RAM  12 . The sample storage area  62  can hold N pieces of biometric information. The biometric information acquisition part  51  repeats command output and storage of biometric information input as a result of the corresponding command output N times, thereby storing N pieces of biometric information into the sample storage area  62 . 
     When the biometric information acquisition part  51  acquires biometric information obtained by being read N times from the biometric information reader  9   a , a user&#39;s finger is preferably taken off the biometric information reader  9   a  after each reading. So, after each reading, a guidance screen prompting the user to take the finger off the biometric information reader  9   a  may be displayed on the display unit  21 , for example. 
     In the first preferred embodiment described below, N is assumed to be three. Accordingly, the biometric information reader  9   a  reads biometric information three times. Then, the biometric information acquisition part  51  inputs three pieces of biometric information from the biometric information reader  9   a  separately, and stores the input biometric information in order into the sample storage area  62 . As a result, three pieces of biometric information D 1 , D 2  and D 3  are stored in the sample storage area  62 . 
     The reference data selection part  52  selects one piece of biometric information from the N pieces (in the first preferred embodiment, three pieces) of biometric information D 1 , D 2  and D 3  acquired by the biometric information acquisition part  51 , and provisionally sets the selected biometric information as reference data to be used in biometric authentication. The reference data selection part  52  first reads the three pieces of biometric information D 1 , D 2  and D 3  stored in the sample storage area  62 , and calculates the respective feature quantities of the biometric information D 1 , D 2  and D 3 . For instance, an image captured by the biometric information reader  9   a  includes a vein pattern as a linear pattern. Then, the reference data selection part  52  first extracts the linear pattern from the image. The reference data selection part  52  then calculates features such as the number of lines and the density of lines constitute the linear pattern, the number of points of intersection of the lines, or the positions of the points of intersection, and sets these values as the feature quantity, for example. That is, in the first preferred embodiment, the feature quantity of biometric information contains several types of data. The feature quantity is not necessarily limited to these values, but may contain other values. 
     After calculating the respective feature quantities of the three pieces of biometric information D 1 , D 2  and D 3 , the reference data selection part  52  evaluates the feature quantity of each of the biometric information D 1 , D 2  and D 3 , and selects one piece of biometric information optimally applied to be used in biometric authentication. In the first preferred embodiment, one piece of biometric information is selected based on the distribution of the respective feature quantities of the biometric information D 1 , D 2  and D 3 . As an example, when the feature quantity contains several types of data, and virtual multi-dimensional space with the number of dimensions corresponding to the number of types of data is given, the feature quantity of each of the biometric information D 1 , D 2  and D 3  is found at a position defined by coordinate values corresponding to the respective values of the several types of data of each feature quantity. Then, the reference data selection part  52  selects one piece of biometric information found at the closest position to the center in this feature distribution. 
       FIGS. 5A and 5B  conceptually show the processing executed by the reference data selection part  52  when the distribution of the respective feature quantities of the biometric information D 1 , D 2  and D 3  is represented two-dimensionally. When the three feature quantities respectively calculated from the three pieces of biometric information D 1 , D 2  and D 3  found as shown in  FIG. 5A , the reference data selection part  52  selects one piece of biometric information found at the closest position to the center in the distribution of the three feature quantities. As an example, with regard to each of the three pieces of biometric information D 1 , D 2  and D 3 , the reference data selection part  52  calculates the sum of the squares of distances from the feature quantity of one piece of the biometric information D 1 , D 2  and D 3  to other feature quantities of the remaining pieces of the biometric information D 1 , D 2  and D 3 . Then, the reference data selection part  52  determines biometric information which has the smallest value of sum as the one found at the closest position to the center of the three pieces of biometric information. So, in the case of  FIG. 5A , the feature quantity of the biometric information D 2  is determined to be at a position nearest to the center as shown in  FIG. 5B  after the calculation described above is executed. Then, the reference data selection part  52  selects the biometric information D 2 , and provisionally sets the biometric information D 2  thereby selected as the reference data BD. 
     After the reference data selection part  52  provisionally sets the reference data BD, the reference data BD is transmitted to the authentication test execution part  53 . Next, the authentication test execution part  53  comes into operation. 
     The authentication text execution part  53  causes the biometric information reader  9   a  to read biometric information once to acquire authentication-testing biometric information, and executes an authentication test by checking the authentication-testing biometric information thereby acquired against the reference data BD. As well as the biometric information acquisition part  51 , by outputting a command to the biometric information reader  9   a  to start reading, the authentication test execution part  53  causes the biometric information reader  9   a  to read biometric information. After outputting the command, the authentication test execution part  53  inputs the authentication-testing biometric information DT obtained by reading the finger vein pattern of a user from the biometric information reader  9   a , and stores the input biometric information DT into the authentication-testing storage area  63  in the RAM  12 . The authentication-testing storage area  63  can hold only one piece of authentication-testing biometric information DT. 
     Thereafter the authentication test execution part  53  compares the authentication-testing biometric information DT and the reference data BD to execute an authentication test. More specifically, the authentication test execution part  53  calculates the feature quantity of the authentication-testing biometric information DT, and compares the calculated feature quantity with the feature quantity of the reference data BD. This comparison in the feature distribution is also made. 
       FIG. 6  conceptually shows the processing executed by the authentication test execution part  53  when the feature distribution is represented two-dimensionally. When the respective feature quantities of the authentication-testing biometric information DT and the reference data BD found as shown in  FIG. 6 , the authentication test execution part  53  obtains a distance LT between these two feature quantities. Then, based on the distance LT, the authentication test execution part  53  determines whether or not a user who entered the authentication-testing biometric information DT is the same user as the one who entered the biometric information D 2  corresponding to the reference data BD, thereby authenticating the user. 
     In order to execute this authentication, the authentication test execution part  53  holds first and second threshold values TH 1  and TH 2  as shown in  FIG. 4 . The first and second threshold values TH 1  and TH 2  are values predetermined to reach the relation as the first threshold value TH 1  being greater than the second threshold value TH 2  between each other. 
     The first threshold value TH 1  is used to determine whether the authentication results in success or failure. If the distance LT between the feature quantities of the authentication-testing biometric information DT and the reference data BD shown in  FIG. 6  is equal to or not greater than the first threshold value TH 1 , the authentication-testing biometric information DT is close to the reference data BD. So, the authentication results in success in this case. In contrast, if the distance LT is greater than the first threshold value TH 1 , the authentication-testing biometric information DT is not close to the reference data BD. So, authentication results in failure in this case. That is, whether the authentication executed by the authentication test execution part  53  results in success or failure is determined by the comparison between the distance LT between the feature quantities of the authentication-testing biometric information DT and the reference data BD, and the first threshold value TH 1 . 
     The second threshold value TH 2  is used to evaluate the reliability of the reference data BD when authentication results in success in the authentication test. It is assumed that the distance LT between the feature quantities of the authentication-testing biometric information DT and the reference data BD is greater than the second threshold value TH 2 , but is equal to or not greater than the first threshold value TH 1 . In this case, even though authentication results in success in the authentication test, the feature quantity of the authentication-testing biometric information DT is found at a position slightly inside a range of which authentication is deemed to be successful. Thus, authentication may result in failure in a next test due to the posture of a finger, for example. The degree of reliability of the reference data BD may be low in this case. So, when the reference data BD registered as the one to be used in actual biometric authentication, false authentication may occur often. 
     In contrast, it is assumed that the distance LT is equal to or not greater than the second threshold value TH 2 . In this case, authentication results in success in the authentication test, and the feature quantity of the authentication-testing biometric information DT is found at a position sufficiently inside the range of which authentication is deemed to be successful. So, the reference data BD is proved to be appropriate reference data to be used in actual biometric authentication. 
     After executing the authentication test described above, the authentication test execution part  53  displays a result of authentication on the display unit  21 . Even when authentication results in success but the degree of reliability of the reference data BD is low, the authentication test execution part  53  displays notification prompting a user to execute the authentication test again. If authentication results in failure, or if the user instructs to perform the authentication test again, the authentication test execution part  53  repeats the authentication test described above. 
     The reference data optimization part  54  comes into operation after the authentication test execution part  53  executes the authentication test described above at least once. The reference data optimization part  54  selects one piece of biometric information from (N+1) pieces (in the first preferred embodiment, four pieces) of biometric information including the N pieces (in the first preferred embodiment, three pieces) of biometric information D 1 , D 2  and D 3  acquired by the biometric information acquisition part  51  and stored in the sample storage area  62 , and the authentication-testing biometric information DT acquired by the authentication test execution part  53  and stored in the authentication-testing storage area  63 , thereby optimizing the reference data BD. That is, the reference data optimization part  54  calculates the respective feature quantities of the four pieces of biometric information D 1 , D 2  and D 3 , and of the authentication-testing biometric information DT in the same way as described above, and evaluates the calculated feature quantities. Thereafter the reference data optimization part  54  selects one piece of biometric information from the four pieces of biometric information D 1 , D 2 , D 3  and DT, and sets the selected biometric information as the reference data BD again. This makes the reference data BD to come closer to the center in the distribution of the feature quantities of biometric information, thereby optimizing the reference data BD. 
       FIGS. 7A and 7B  conceptually show the processing executed by the reference data optimization part  54  when the distribution of the respective feature quantities of the biometric information D 1 , D 2 , D 3  and DT is represented two-dimensionally. When the four feature quantities respectively calculated from the four pieces of biometric information D 1 , D 2 , D 3  and DT are found as shown in  FIG. 7A , the reference data optimization part  54  selects one piece of biometric information found at the closest position to the center in the distribution among the four feature quantities. This selection is described in more detail as follows. As well as the processing executed by the reference data selection part  52 , with regard to each of the four pieces of biometric information D 1 , D 2 , D 3  and DT, the reference data optimization part  54  calculates the sum of the squares of distances from the feature quantity of one piece of the biometric information D 1 , D 2 , D 3  and DT to other feature quantities of the remaining pieces of the biometric information D 1 , D 2 , D 3  and DT. Then, the reference data optimization part  54  determines that biometric information the sum of which is the smallest as the one found at the closest position to the center of the four pieces of biometric information. So, in the case of  FIG. 7A , by executing the above described calculation, the feature quantity of the biometric information DT acquired to be used in the authentication test is determined to be at the closest position to the center as shown in  FIG. 7B . Then, the reference data optimization part  54  selects the biometric information DT, and sets the biometric information DT thereby selected as the reference data BD again. This processing makes the reference data BD to come closer to the center in the feature distribution, so that this reference data BD has a higher degree of appropriateness than the reference data used in the previous authentication test has. Thus, when the reference data BD optimized by the reference data optimization part  54  is applied as the reference data BD to be used in actual biometric authentication, the frequency of the occurrence of false authentication may be decreased in actual biometric authentication compared with the case where reference data selected by the reference data selection part  52  is applied. By repeating the process described above, the reference data BD will have a higher and higher degree of appropriateness. 
     After the reference data BD is optimized in the manner described above, the reference data optimization part  54  selects one piece of biometric information as inappropriate data from the four pieces of biometric information. In contrast to the optimization of the reference data BD, biometric information corresponding to a feature quantity found at the farthest position from the center in the distribution of the feature quantities of the four pieces of biometric information is selected here. That is, of the four pieces of biometric information D 1 , D 2 , D 3  and DT for which respective feature quantities are calculated, one piece of biometric information is selected that has a maximum sum of the squares of distances from its feature quantity to other feature quantities of the remaining pieces of the biometric information D 1 , D 2 , D 3  and DT. So, biometric information that has the lowest degree of appropriateness to be set as reference data is selected from the four pieces of biometric information D 1 , D 2 , D 3  and DT as inappropriate data. In the case of  FIG. 7A , for example, the feature quantity of the biometric information D 3  is determined to be at the farthest position from the center as shown in  FIG. 7B  by executing the calculation described above. So, the biometric information D 3  is selected as inappropriate data. Then, the reference data optimization part  54  deletes the biometric information selected as inappropriate data from the biometric information storage area  61 , and stores the remaining three pieces of biometric information into the sample storage area  62 . 
     As described above, the reference data optimization part  54  selects inappropriate data from the four pieces of biometric information D 1 , D 2 , D 3  and DT, and deletes the selected inappropriate data. So, for optimizing reference data again even after the authentication test execution part  53  executes the authentication test several times, the reference data optimization part  54  selects the optimum reference data BD from the four pieces of biometric information D 1 , D 2 , D 3  and DT as described above. That is, the reference data optimization part  54  does not need to refer to more than four pieces of biometric information D 1 , D 2 , D 3  and DT for optimization. This advantageously realizes efficient processing, leading to shorter time required for the optimization. This advantage is also taken when the function of the reference data optimization art part  54  is realized in hardware. In this case, the number of pieces of data to be referred to is fixed at four, and hardware configuration is easy to be developed. 
     The reference data transmission part  55  transmits the reference data BD optimized by the reference data optimization part  54  as described above to the image processing device  3 , and registers the reference data BD as the one to be used in actual biometric authentication in the image processing device  3 . When the reference data optimization part  54  does not optimize the reference data BD, the reference data BD provisionally set by the reference data selection part  52  is transmitted as it is to the image processing device  3 . 
     Next, the operation of the information processing device  2  is described in detail.  FIGS. 8 to 10  are flow diagrams explaining an exemplary process sequence executed by the CPU  11  in the information processing device  2  based on the program  18 .  FIGS. 11A and 11B ,  FIGS. 12A and 12B , and  FIGS. 13A and 13B  show examples of screens displayed on the display unit  21  during the course of the process. 
     Upon the start of the process based on the program  18  in the information processing device  2 , a count N is reset to “zero” (step S 10 ) at first, and an initial screen is displayed on the display unit  21  (step S 11 ).  FIG. 11A  shows an example of the initial screen. A user who intends to register the reference data BD operates the manipulation input unit  24  to enter his or her own user name and the like into a user name entry field  21   a , operates the mouse  23  to move a pointer  21   m , and clicks a start reading button  21   c , thereby starting the reading of biometric information. The screen on the display unit  21  includes an information display field  21   b  for displaying the status of process of registering reference data, etc. In the initial state, the screen shows that the reading operation of biometric information is unexecuted. Also, the screen shows an authentication test button  21   d , a retest button  21   e , a register button  21   f , and a cancel button  21   g  operable by a user. The authentication test button  21   d , the retest button  21   e  and the register button  21   f  are shown to be inoperable in the initial state of the screen. The cancel button  21   g  is intended for example to complete the execution of the program  18 . 
     A user clicks the start reading button  21   c  with placing his or her finger over the biometric information reader  9   a  (see  FIG. 3B ), in response to which the information processing device  2  reads biometric information once (step S 12 ). If biometric information is successfully acquired, the information processing device  2  stores the acquired biometric information into the sample storage area  62  (step S 13 ). Then, the information processing device  2  increments the count N by “one” (step S 14 ), and determines whether or not the count N has reached “three” (step S 15 ). If the count N has not reached “three,” the information processing device  2  repeats the process from steps S 12  to S 14  until the count N reaches “three.” As a result, three pieces of biometric information D 1 , D 2  and D 3  are stored in the sample storage area  62 . When biometric information is read repeatedly, the user preferably takes the finger off the biometric information reader  9   a  after each reading. 
       FIG. 11B  shows a display screen at the time of biometric information is read twice. The state that “OK” is shown after each reading means that a linear pattern (vein pattern) has successfully been extracted from the read biometric information. So, when the state that “NG” is shown after the reading, the user is required to perform reading operation of biometric information again. 
     After biometric information is successfully read three times (if a result of step S 15  is YES), an operation for calculating the respective feature quantities of the three pieces of biometric information D 1 , D 2  and D 3  follows (step S 16 ). After the respective feature quantities are calculated, one piece of biometric information is selected based on the distribution of the respective feature quantities of the three pieces of biometric information D 1 , D 2  and D 3 . Thereafter the selected biometric information is provisionally set as the reference data BD (step S 17 ). 
     The display screen on the display unit  21  at this stage is the one shown in  FIG. 12A . In this screen, the start reading button  21   c  becomes inoperable, while the authentication test button  21   d  becomes operable. Further, information prompting the user to perform an authentication test appears in the information display field  21   b . Then, the user clicks the authentication test button  21   d  with the mouse  23 , by which the information processing device  2  is instructed to start the authentication test. 
     The information processing device  2  is placed in standby until an instruction to start the authentication test is given (step S 18 ). When the user clicks the authentication test button  21   d  with placing his or her finger over the biometric information reader  9   a  (if a result of step S 18  is YES), the information processing device  2  reads biometric information once (step S 19 ). Then, the information processing device  2  stores the biometric information DT thereby acquired into the authentication-testing storage area  63  (step S 20 ). Thereafter the information processing device  2  executes an operation for calculating the feature quantity of the authentication-testing biometric information DT (step S 21 ). After the calculation, the information processing device  2  compares the feature quantity of the authentication-testing biometric information DT with that of the reference data BD set at this stage to authenticate the user (step S 22 ). In step S 22 , the distance LT between two feature quantities is obtained in the feature distribution, and the obtained distance LT and the first threshold value TH 1  are compared as described, thereby authenticating the user. At this time, the distance LT is also compared with the second threshold value TH 2 . 
     Next, with reference to the flow diagram of  FIG. 9 , it is determined whether or not the authentication ends in success (step S 30 ). If it is determined that the authentication ends in failure (if a result of step S 30  is NO), the flow moves on to step S 37  in which an authentication failure screen is displayed on the display unit  21 . If it is determined that the authentication ends in success (if a result of step S 30  is YES), it is also determined whether or not the reference data BD set at this stage has a high degree of reliability (step S 31 ). This determination is made based on a result of comparison between the distance LT and the second threshold value TH 2 . If the reference data BD is determined to have a high degree of reliability (if a result of step S 31  is YES), the flow moves on to step S 32  in which a registration confirmation screen is displayed on the display unit  21 . If the reference data BD is determined to have a low degree of reliability (if a result of step S 31  is NO), the flow moves on to step S 35  in which a retest recommendation screen is displayed on the display unit  21 . 
       FIG. 12B  is an example of the registration confirmation screen displayed in step S 32 . This registration confirmation screen is displayed when the authentication ends in success in the authentication test, and when the reference data BD set at this stage has a high degree of reliability. So, a sign checking to see whether or not the reference data BD set at this stage is to be registered appears in the information display field  21   b . In order to register the reference data BD, the user clicks the register button  21   f . The authentication test can also be performed repeatedly on this registration confirmation screen. If the user wants to perform the authentication test again, the user clicks the authentication test button  21   d.    
       FIG. 13A  is an example of the retest recommendation screen displayed in step S 35 . This retest recommendation screen is displayed when the authentication ends in success in the authentication test, but when the reference data BD set at this stage is determined to have a low degree of reliability. So, a sign prompting the user to perform a retest appears in the information display field  21   b . If the user would like to perform a retest, the user clicks the retest button  21   e . The authentication ends in success in the authentication test even when the retest recommendation screen is displayed. Therefore the user may register the reference data BD set at this stage as it is. The user clicks the register button  21   f  in order to register the reference data BD at this stage. 
       FIG. 13B  is an example of the authentication failure screen displayed in step S 37 . This authentication failure screen is displayed when authentication results in failure in the authentication test. So, the reference data BD set at this stage cannot be registered as it is, and the register button  21   f  is shown to be inoperable. Thus, the user should perform the authentication test again by clicking the retest button  21   e.    
     Returning to  FIG. 9 , after displaying the record confirmation screen in step S 32 , the information processing device  2  determines whether or not the register button  21   f  has been clicked (step S 33 ). If the register button  21   f  was clicked, the information processing device  2  transmits the reference data BD set at this stage to the image processing device  3 , and registers the transmitted reference data BD in the image processing device  3  (step S 34 ). In contrast, if the user clicks the authentication test button  21   d , a result of step S 33  is NO. So, the flow returns to step S 18  of  FIG. 8  to start the authentication test again. 
     When the retest recommendation screen is displayed in step S 35 , the information processing device  2  determines whether or not the retest button  21   e  has been clicked (step S 36 ). If the retest button  21   e  was clicked (if a result of step S 36  is YES), the information processing device  2  executes reference data optimization (step S 40 ) as described in detail later. After the reference data optimization (step S 40 ), the flow returns to step S 18  of  FIG. 8  to start the authentication test again. In contrast, if the register button  21   f  was clicked on the retest recommendation screen, a result of step S 36  is NO, and a result of step S 33  is YES. So, the information processing device  2  transmits the reference data BD set at this stage to the image processing device  3 , and registers the transmitted reference data BD in the image processing device  3  (step S 34 ). 
     When the authentication failure screen is displayed in step S 37 , the information processing device  2  is caused to execute the reference data optimization by the click of the retest button  21   e  (step S 40 ). After the reference data optimization (step S 40 ), the flow returns to step S 18  to start the authentication test again. 
       FIG. 10  is a flow diagram explaining the process sequence of the reference data optimization (step S 40 ) in detail. When the reference data optimization is started, the information processing device  2  retrieves the four pieces of biometric information D 1 , D 2 , D 3  and DT from the RAM  12  (step S 41 ), and calculates the respective feature quantities of the biometric information D 1 , D 2 , D 3  and DT (step S 42 ). When the feature quantities calculated in steps S 16  and S 21  are held for example in the RAM  12 , the processing of step S 42  is not necessary to be executed. Then, based on the respective feature quantities of the four pieces of biometric information D 1 , D 2 , D 3  and DT, one appropriate piece of biometric information is selected from the four pieces of biometric information D 1 , D 2 , D 3  and DT, and the selected biometric information is set as the reference data BD again. Thus, biometric information having a feature quantity found at the closest position to the center in the distribution of the feature quantities is selected and then set as the reference data BD, thereby optimizing the reference data BD. 
     After the more appropriate reference data BD is selected, the information processing device  2  selects one piece of biometric information as inappropriate data from the four pieces of biometric information D 1 , D 2 , D 3  and DT (step S 44 ), and deletes the selected biometric information corresponding to the inappropriate data from the biometric information storage area  61  (step S 45 ), thereby updating the biometric information storage area  61  in the RAM  12  (step S 46 ). The reference data optimization (step S 40 ) is completed here. 
     The process sequence described above allows to execute the authentication test repeatedly. By sequentially repeating the authentication test and the reference data optimization (step S 40 ), the reference data BD becomes the one having a higher degree of appropriateness. This works especially on the case where the authentication ends in failure in the authentication test. In this case, while the reference data BD set at the stage of failure may not be appropriate data, the reference data optimization (step S 40 ) is executed without fail. So, data having a higher degree of appropriateness can be set again as the reference data BD. In the example described above, the reference data optimization (step S 40 ) is not performed if the information processing device  2  is instructed to execute the authentication test again in a condition where the authentication test results in success, and the degree of reliability of the reference BD is determined to be high. However, the reference data optimization (step S 40 ) may also be executed in this case. 
     As described above, in the information processing device  2  of the first preferred embodiment, one piece of biometric information is selected from the three pieces of biometric information D 1 , D 2  and D 3  acquired first as a result of three times of reading operations, and the selected biometric information is provisionally set as the reference data BD. Thereafter the authentication test is executed to determine whether or not the reference data BD provisionally set has the highest degree of appropriateness. If the reference data BD provisionally set does not have the highest degree of appropriateness, the reference data BD having a higher degree of appropriateness is selected from the four pieces of biometric information D 1 , D 2  and D 3 , and DT acquired to be used in the authentication test. Thus, the reference data BD can be optimized before being registered in the image processing device  3 . 
       FIG. 14  is a block diagram showing the configuration of functions in the controller  40  of the image processing device  3 . As shown in  FIG. 14 , the controller  40  of the image processing device  3  functions as a reference data registering part  71  and a biometric authentication processor  72 . 
     The reference data registering part  71  receives the reference data BD generated by the information processing device  2  by executing the process described above through the network  4 , and stores the received reference data BD into the storage unit  45 . 
     The biometric authentication processor  72  acquires the biometric information of a user who tries to use the image processing device  3  from the biometric information reader  9   b , and compares the acquired biometric information with the reference data BD stored in the storage unit  45 , thereby authenticating the user. This authentication follows the same process as that of the authentication in the authentication test executed by the information processing device  2 . That is, the biometric authentication processor  72  holds the first threshold value TH 1  applied for executing the authentication. If the distance LT between the feature quantities of the biometric information acquired from the biometric information reader  9   b  and the reference data BD is equal to or not greater than the first threshold value TH 1 , it is determined the authentication ends in success. If the distance LT is greater than the first threshold value TH 1 , it is determined the authentication ends in failure. 
     When it is determined that the authentication ends in success, the biometric authentication processor  72  enables a function relating to image processing for which an authenticated user has been authorized in advance, thereby allowing a user to use the image processing device  3 . 
     The reference data BD referred to in this actual biometric authentication in the image processing device  3  has been optimized as a result of the above-described processing executed in the information processing device  2 . So, compared to conventional biometric authentication, this reduces the incidence of false authentication in which causing authentication of a user to be ended in failure even when the user is a rightful user. Thus, when user authentication in the image processing device  3  employs biometric authentication as in the first preferred embodiment, the security level of the image processing device  3  is raised without deteriorating the operability of the image processing device  3 . 
     As described above, according to the first preferred embodiment, one piece of biometric information is selected from N pieces of biometric information, and the selected biometric information is provisionally set as reference data. Thereafter biometric information to be used in an authentication test is acquired to execute the authentication test. So, the appropriateness of the reference data provisionally set is determined. Further, one piece of biometric information is selected from (N+1) pieces of biometric information including the N pieces of biometric information, and the authentication-testing biometric information, and the reference data is optimized. So, data having a higher degree of appropriateness than the reference data provisionally set is set as reference data. As a result, it may determine in advance whether or not biometric information has the highest degree of appropriateness is selected as the reference data, and the reference data can be optimized at the time of registering the reference data to be used in biometric authentication. Thus, the incidence of false authentication in actual biometric authentication can be reduced compared to conventional biometric authentication. 
     Second Preferred Embodiment 
     A second preferred embodiment of the present invention is described next. In the first preferred embodiment described above, the reference data BD to be used in actual biometric authentication in the image processing device  3  is generated in the information processing device  2  set separately from the image processing device  3 . In the second preferred embodiment, the above-described function of the information processing device  2  is incorporated as it is into an image processing device, so the image processing device can independently register the reference data BD, and optimize the reference data BD. 
       FIG. 15  is a block diagram showing the configuration of functions in the controller  40  of the image processing device  3  according to the second preferred embodiment. In the second preferred embodiment, the CPU  41  in the controller  40  executes the program stored in the hard disk drive  38  (see  FIG. 2 ), in response to which the controller  40  becomes operative to function in a way shown in  FIG. 15 . That is, when the reference data BD to be used in actual biometric authentication is registered in the image processing device  3 , the controller  40  of the second preferred embodiment becomes operative to function as the biometric information acquisition part  51 , the reference data selection part  52 , the authentication test execution part  53 , the reference data optimization part  54 , and the reference data registering part  71 . The detail of each of these parts is the same as that described in the first preferred embodiment. The process sequence executed by bringing each part into operation is also the same as that shown in the flow diagrams explained in the first preferred embodiment. 
     Therefore, in the image processing device  3  of the second preferred embodiment, when the reference data BD is registered, the three pieces of biometric information D 1 , D 2  and D 3  are acquired first from the biometric information reader  9   b . Then, one piece of biometric information is selected from the three pieces of biometric information, and the selected biometric information is provisionally set as the reference data BD. Thereafter an authentication test is executed to determine whether or not the reference data BD provisionally set is appropriate data. If the reference data provisionally set is not appropriate data, another piece of biometric information has higher degree of appropriateness is selected from the four pieces of biometric information including the three pieces of biometric information D 1 , D 2  and D 2 , and the biometric information DT acquired to be used in an authentication test, and the selected biometric information is set as the reference data BD. Finally, the reference data registering part  71  stores the optimized reference data BD into the storage unit  45 . 
     In actual biometric authentication in the image processing device  3 , user authentication is executed by making reference to the optimized reference data BD stored in the storage unit  45 . So, compared to conventional biometric authentication, this reduces the incidence of false authentication in which authentication of a user ends in failure even when the user is a rightful user. 
     As described, in the second preferred embodiment, the reference data BD to be used in biometric authentication is registered after being optimized even when the image processing device  3  is set independently. Thus, the second preferred embodiment can preferably be applied to the case where the image processing device  3  is used independently. 
     In order to incorporate the function of the information processing device  2  described in the first preferred embodiment into the image processing device  3 , each part shown in  FIG. 15  may be realized in hardware. In this case, the number of pieces of biometric information to be referred to in each part can always be fixed at a certain number, thereby making hardware configuration relatively easy. 
     (Modifications) 
     While the preferred embodiments of the present invention have been described above, the present invention is not limited to these preferred embodiments. Various modifications may be applied to the present invention. By way of example, in the preferred embodiments described above, the reading of the finger vein pattern of a user is explained as an exemplary way of biometric authentication. A palm vein pattern may alternatively be read. Still alternatively, a fingerprint may be read as biometric information other than a vein pattern. 
     In the preferred embodiments described above, the number of times N that biometric information is read at first in order to set the reference data BD is predetermined at “three.” The number N can suitably be set in consideration of the time required for calculation, etc. However, in the above-described preferred embodiments, one piece of biometric information found at the closest position to the center in the distribution of the features quantities of the N pieces of biometric information is selected. So, the number N should be an integer of 3 or greater. 
     In the preferred embodiments described above, the image processing device  3  is shown to be a device having several functions relating to image processing such as those of a copier, a scanner, a FAX, a printer, and others. However, the image processing device  3  is not necessarily a device having several functions. The image processing device  3  may be a copier-only device or a scanner-only device. Moreover, the image processing device  3  may be a FAX-only device or a printer-only device. Still alternatively, the image processing device  3  may be a device has an image processing function except those described above. 
     While the invention has been shown and described in detail, the foregoing description is in all aspects illustrative and not restrictive. It is therefore understood that numerous modifications and variations can be devised without departing from the scope of the invention.