1. A face authentication system, comprising: a reflectance image generating unit for generating a blurred image of an input image based on the input image including a face of a person and generating an input reflectance image by separating each corresponding pixel value of the blurred image from each pixel value of the input image; and a face authenticating unit for performing face authentication of the face of the person included in the input image by comparing the input reflectance image with a registered reflectance image of a previously registered person.