An image processing apparatus that performs image registration processing between a plurality of images through a motion vector calculation sets a plurality of motion vector measurement regions on an image, calculates a motion vector in each of the plurality of motion vector measurement regions, specifies a region of interest on the image, determines whether or not each of the plurality of motion vector measurement regions is included in the region of interest, calculates a contribution of each motion vector such that the contribution of the motion vector of a motion vector measurement region included in the region of interest is larger than the contribution of the motion vector of a motion vector measurement region not included in the region of interest, and determines an inter-image motion vector by integrating the motion vectors calculated respectively in the plurality of motion vector measurement regions in accordance with the calculated contribution.