1. An imaging system for imaging a subject, comprising: a plurality of imaging devices, provided at different positions, respectively, operable to image said subject; a direction detection unit operable to detect a moving direction of said subject based on two or more images of said subject taken at different times by one of said plurality of imaging devices; a selection unit operable to select one of said plurality of imaging devices, that is to capture an authentication image of said subject, based on said moving direction detected by said direction detection unit and said positions of said plurality of imaging devices; and a storage unit operable to store said authentication image captured by said selected one of said plurality of imaging devices.