1. A masquerading detection system comprising: an imaging unit obtaining a first two-dimensional image by imaging an inspection object from a first angle, and a second two-dimensional image by imaging the inspection object from a second angle which is different from the first angle; a feature point coordinate calculating unit detecting first feature points from the first two-dimensional image, obtaining first feature point coordinates representing positions of the detected feature points, detecting second feature points from the second two-dimensional image, and obtaining second feature point coordinates representing positions of the detected feature points; a feature point associating unit associating the first feature points with the second feature points; a feature transforming unit obtaining transformed coordinates by performing a plane projective transformation for the second feature point coordinates from the second two-dimensional image to the first two-dimensional image; a similarity determining unit obtaining a difference between the transformed coordinates and the first feature point coordinates and determining that masquerading has been attempted when the obtained difference is equal to or smaller than a predetermined value; and a plane transformation matrix estimating unit determining a transformation matrix from the second two-dimensional image to the first two-dimensional image with the use of the first feature point coordinates and the second feature point coordinates, wherein said feature transforming unit performs the projective transformation with the use of the transformation matrix, and wherein the transformation matrix is a homography matrix.