A registration processing apparatus generates a polynomial to calculate a value corresponding to a distance from the surface of a target object in a first image, and acquires a plurality of position coordinates on the surface of the target object in a second image. Then the apparatus respectively calculates a value corresponding to the distance from the surface of the target object in the first image using the polynomial, for position coordinates obtained by coordinate conversion of the plurality of position coordinates. The apparatus coordinate-converts the position coordinates of the second image by a coordinate conversion method for the plurality of position coordinates determined based on the calculated values.