1. An image processing method for overlapping and combining a plurality of images sharing a photograph range, the image processing method comprising: calculating a position shift parameter between the plurality of images; correcting the position shift between the plurality of images using the position shift parameter; evaluating similarity of each portion of the plurality of images after the correction between the plurality of images by calculating a level difference and edge intensity of the portion of the plurality of images; and evaluating the similarity by the level difference and the edge intensity; 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.