1. An authentication system for authenticating a person-to-be-authenticated, comprising: a first photographing section, which is provided in a route passed by the person-to-be-authenticated, which photographs the person-to-be-authenticated to obtain a first image; a first authentication section which correlates the first image of the person-to-be-authenticated photographed by said first photographing section to a correlation image stored in advance of the person-to-be-authenticated having features distinct from features in the first image of the person-to-be-authenticated photographed by said first photographing section and which authenticates the person-to-be-authenticated when the correlation between the first image of the person-to-be-authenticated photographed by said first photographing section and the correlation image is greater than a predetermined threshold; a second photographing section, which is provided at a location through which the person-to-be-authenticated passes, which photographs the person-to-be-authenticated to obtain a second image, wherein said second photographing section is located downstream of said first photographing section in the route passed by the person-to-be-authenticated; and a second authentication section which authenticates the person-to-be-authenticated by correlating the first image of the person-to-be-authenticated photographed by said first photographing section with the second image of the person-to-be-authenticated photographed by said second photographing section, wherein the features distinct from features in the first image of the person-to-be-authenticated by said first photographing section include features of the person-to-be-authenticated that are changed due to aging of the person-to-be-authenticated, wherein said first photographing section photographs a first comparison image in which the person-to-be-authenticated is photographed and of which a photographed area of the first comparison image to be photographed is larger than a photographed area of the correlation image stored in advance of the person-to-be-authenticated, wherein said second photographing section photographs a second comparison image in which the person-to-be-authenticated is photographed and of which a photographed area of the second comparison image is substantially the same as the photographed area of the first comparison image, and wherein said second authentication section authenticates the person-to-be-authenticated by comparing the first comparison image and the second comparison image.