1. A method for detecting image separating points where only a given subject image is separated from images, said method comprising the steps of: a first step for displaying on a screen a plurality of candidate points in the vicinity of a boundary of said given subject image, which are input by a user; a second step for determining and displaying a smooth curve which connects said plurality of candidate points; a third step for determining a rate of change in intensity of each of a plurality of light components of said image having different wavelengths along a straight line normal to said curve at each of said plurality of candidate points; a fourth step for correcting the position of each of said candidate points, respectively, by calculating a corrected position for each of said plurality of candidate points based upon the rate of change in intensity of light determined at each of said plurality of light components of said plurality of candidate points; the calculation of the corrected position of each of said plurality of candidate points includes determining a preliminary corrected point for each of said plurality of light components of each of said plurality of candidate points based on the rate of change in intensity of each of said plurality of light components; and a fifth step for determining and displaying a smooth curve connecting said corrected candidate points.