1. An image processing apparatus comprising: a storage unit which stores data of a plurality of images including an examination target organ of an object; a reference point determining unit which determines, from each of the images, a reference point which is located in or near a region of the examination target organ and undergoes a relatively small displacement accompanying respiratory motion; and a moving amount calculation unit which determines a position of each of a plurality of points of interest included in the region of the examination target organ relative to the reference point for each of the images, and calculates, directly based on the determined positions and the reference point, moving amounts for the corresponding points of interest between the images accompanying the respiratory motion.