1. An image processing method comprising the steps of: making an image region, which includes an eye region having discoloration and which has been designated in advance, to be an xy plane, and obtaining an image characteristic amount for each pixel by using any one of hue, saturation and lightness or a combination of two or more of the hue, the saturation and the lightness; setting a three-dimensional xyz space on whose z axis are plotted the image characteristic amounts, and sectioning the xy plane of each region whose z axis values are distributed in a crest-shape with respect to the spread of the xy plane; and determining a discoloration region of a pupil in accordance with any one of or a combination of two or more of information about the shape, information about the position, information about the surface area and a statistical image characteristic amount on the xy plane of each of the sectional regions, and correcting the region determined to be a discoloration region to an image of a normal eye.