1. An image processing apparatus comprising: a display unit which displays an image; a detection unit which detects a position on the display unit designated from an outside; an original image display unit which displays an original image based on original image data in a first display area on the display unit; a specifying unit which, when a position within the first display area is designated from the outside, specifies a designated region corresponding to the designated position in the first display area based on a detection result of the detection unit; and a combining unit which displays at least a part of an additional image based on additional image data in the designated region in the first display area to display a combined image, in which the original image and the additional image are combined, on the display unit.