To improve the precision with which a false finger formed by attaching a transparent thin film to a surface of a finger is identified, a fingerprint authentication system includes: an image division unit 31 that divides a captured image of an authentication subject to be subjected to fingerprint authentication into a plurality of small regions a frequency analysis unit 32 that performs a frequency analysis on each of the small regions a ridge candidate extraction unit 33 that extracts frequency components corresponding to ridge candidates in the small regions from frequency components obtained in the frequency analysis a continuous ridge candidate group generation unit 34 that compares the ridge candidates between adjacent small regions, and when the ridge candidates satisfy a condition enabling the ridge candidates to be determined continuous, generates a continuous ridge candidate group including the ridge candidates and a determination unit 35 that determines that an abnormality exists in the image when overlap exists between the image regions corresponding to the continuous ridge candidate group.
