1. A method of correcting the contour of a grayscale image based on an image processing process carried out by a computer, comprising the steps of: generating a distance contour image representing a contour extracted from a distance image whose pixels include distance values and a grayscale contour image representing a contour extracted from a grayscale image whose pixels include gradation values, from a subject; determining whether or not there is a contour in a region on said distance contour image whose coordinate position corresponds to that of a region which includes a portion of the contour of said grayscale contour image; and correcting the contour of said grayscale image if it is judged that there is said contour.