As a method for authenticating individuals, biometric authentication is known which utilizes physical characteristics. This is to examine whether a physical characteristic peculiar to each individual, such as a fingerprint or a face, is the same or not that one has been enrolled, and to authenticate an identical person if those are determined to be identical. For example, in a case of fingerprint authentication, a person who would like to be authenticated enrolls a fingerprint data (a template) of him/her for verification in an authentication system in advance, and when the person would like to be authenticated, an inputted fingerprint data and the template are compared, then determination whether it is the enrolled person or not can be done with a magnitude correlation between a verification evaluation value, such as similarity, and a prescribed threshold.
Then, if the threshold is set in a value which is exact too much, a false non-matching rate (an error rate in which identical things are determined as different things) becomes high, which is inconvenient for an authentic enrollee. On the contrary, if the threshold is set in a wider range of values, a false matching rate (an error rate in which different things are determined as identical things) becomes high, which increases a risk where non-enrollee can be authenticated. As described, the false matching rate and the false non-matching rate are determined when the threshold is fixed, and they are in a relationship of trade-off.
A desirable threshold needs to be determined depending on a required quality of authentication system. It is a serious error that the authentication system accepts non-enrollee by mistake, so the false matching rate needs to be lower than a prescribed value in the authentication system which is required security. Accordingly, the threshold needs to be determined so as to reach a required false matching rate.
the relationship between the threshold and the false matching rate can be obtained by verifying a large number of data for test practically to examine the false matching rates in cases with various thresholds, as shown in Non-patent document 1. If the threshold is determined to satisfy the required false matching rate in the authentication system, the error rate of accepting a non-enrollee can be equal to a required value or less.
However, the threshold determined as in the above is determined in order that an average false matching rate of all data is to be equal to the required value or less, while the false matching rates for each data are different according to the data. Accordingly, the thresholds need to be determined so that the false matching rates for each data can be evaluated. In the individual authentication method described in Patent Document 1, relationships between thresholds and false matching rates/false non-matching rates at each individual are obtained and the thresholds are determined so that a problem where the false matching rates or the false non-matching rates becomes to be different depending on individuals is solved.    Non-Patent Document 1: Japanese Industrial Standards Committee (JISC), TS/TR number “X0053”, TS/TR name “Evaluation method for accuracy of fingerprint authentication systems”    Patent-Document 1: Japanese Patent Application Laid-open No. 2001-21309
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