Face authentication apparatus

1. A face authentication apparatus comprising:

at least one memory configured to store instructions; and

at least one processor configured to execute the instructions to:

acquire a face image of an authentication target;

perform face authentication by calculating similarity between face information based on the face image of the authentication target and reference face information of each of a plurality of registered users;

compare the similarity with a threshold;

calculate an average similarity value on a success result of the face authentication of the plurality of registered users;

generate an approximation function representing a change in the similarity as a function of time;

predict a change in the similarity based on the generated approximation function;

change the threshold based on a result of the prediction.

2. The face authentication apparatus according to claim 1 , wherein the at least one processor configured to execute to:

change the threshold based on a prediction result of the change in the average similarity value.

3. The face authentication apparatus according to claim 1 , wherein

the threshold is a common threshold set to the plurality of the registered users.

4. The face authentication apparatus according to claim 1 , wherein

the threshold is a threshold set to each of the plurality of registered users.

5. The face authentication apparatus according to claim 1 , wherein the at least one processor configured to execute to:

classify similarity values in similarity history on the success result of the face authentication of the plurality of registered users into a plurality of groups based on authentication time.

6. The face authentication apparatus according to claim 1 , wherein generate the approximation function based on the average similarity.

7. The face authentication apparatus according to claim 1 , wherein the calculating the average similarity value by the at least one processor further comprises:

calculating a first average similarity value corresponding to the success result of the face authentication of the plurality of registered users in a first time period; and

calculate a second average similarity value corresponding to the success result of the face authentication of the plurality of registered users in a second time period.

8. The face authentication apparatus according to claim 7 , wherein the at least one processor is further configured to generate the approximation function based on the first average similarity value and the second average similarity value.

9. The face authentication apparatus according to claim 7 , wherein the at least one processor is further configured to generate the approximation function based on the first average similarity value and the second average similarity value by performing a fitting operation using least-square method.

10. The face authentication apparatus according to claim 1 , wherein the at least one processor is further configured to:

determine a predicted future average similarly value based on the approximation function;

calculate a difference between the predicated average similarity value and the threshold;

based on a determination that the difference is greater than a preset value, decrease the threshold; and

based on a determination that the difference is less than a preset value, increase the threshold.

11. A face authentication method comprising:

acquiring a face image of an authentication target;

performing face authentication by calculating similarity between face information based on the face image of the authentication target and reference face information of each of the plurality of registered users;

comparing the similarity with a threshold;

calculating an average similarity value on a success result of the face authentication of the plurality of registered users;

generating an approximation function representing a change in the similarity as a function of time;

predicting a change in the similarity based on the generated approximation function;

changing the threshold based on a result of the prediction.

12. A non-transitory computer-readable medium storing a program comprising instructions for causing a computer, including a processor and a memory, to perform processing to:

acquire a face image of an authentication target;

perform face authentication by calculating similarity between face information based on the face image of the authentication target and reference face information of each of the plurality of registered users;

compare the similarity with a threshold;

calculate an average similarity value on a success result of the face authentication of the plurality of registered users;

generate an approximation function representing a change in the similarity as a function of time;

predict a change in the similarity based on the generated approximation function;

change the threshold based on a result of the prediction.