1. An image processing apparatus for combining objects included in a plurality of images into one image, the image processing apparatus comprising: a specification unit configured to, based on a reference image out of a plurality of images and a plurality of comparative images out of the plurality of images, specify a difference region in each of the plurality of comparative images, including an object subjected to combination corresponding to a difference from the reference image; a determination unit configured to, based on a plurality of difference regions specified in the plurality of comparative images by the specification unit, determine an object region corresponding to an object included in the reference image; and a combination unit configured to, based on the object region in the reference image determined by the determination unit and the plurality of difference regions in the plurality of comparative images, combine, with the reference image, the objects subjected to combination included in the plurality of difference regions so that an object corresponding to the object region is included in the reference image with which the plurality of difference regions are combined.