1. An image processing apparatus comprising: a search unit configured to search a plurality of corresponding points in a second image that correspond to a plurality of points in a first image respectively; a calculating unit configured to generate groups, each including a part of the plurality of corresponding points based on a distance between each of the plurality of points in the first image and the respective corresponding points in the second image, and to calculate a coordinate transformation coefficient corresponding to each generated group, wherein the calculating unit: generates a first group including a first part of the plurality of corresponding points in the first image and a second group including a second part of the plurality of corresponding points in the first image and not included in the first group, and calculates a first coordinate transformation coefficient corresponding to the first group and a second coordinate transformation coefficient corresponding to the second group; and a synthesizing unit configured to generate a synthesis image, using at least one generated coordinate transformation coefficient and the second image.