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; a storage unit operable to store said authentication image captured by said selected one of said plurality of imaging devices; and an authentication unit operable to authenticate said subject based on said authentication image stored in said storage unit; wherein said selection unit detects a frontal direction of said subject based on said moving direction detected by said direction detection unit and selects one of said plurality of imaging devices, that is able to image a front view of said subject, based on said positions of said plurality of imaging devices, said selection unit selects said one of said plurality of imaging devices, that is to capture said authentication image of said subject, based on said detected moving direction, said detected moving direction used to calculate a position to which said subject will move to, and based on positional information related to said position of each of said plurality of imaging devices, and said selection unit determines which one of said plurality of imaging devices to select by detecting said frontal direction of said subject and determining which one of said plurality of imaging devices is near said calculated position to which said subject will move to based on said positional information related to said position of each of said plurality of imaging devices and is in a position to capture said front view of said subject, said selection unit initializes said one of said plurality of imaging devices to capture said authentication image of said subject.