1. An image processing method for overlapping and combining a plurality of images sharing a photograph range, comprising: a position shift detection step of calculating a position shift parameter between the plurality of images; a position shift correction step of correcting the position shift between the plurality of images using the position shift parameter; a similarity evaluation step of evaluating similarity of each portions of the plurality of images after the correction between the plurality of images; and a combining step of changing a combining method or a, combining parameter of the plurality of images according to the similarity evaluation result and combining the plurality of images after the correction by the changed combining method or a combining parameter.