1. An image processing apparatus comprising: an image receiving unit that receives a first image and a second image; a first specified area specifying unit that allows a user to specify a first specified area within the first image; a first comparison area setting unit that sets a first comparison area within the first image on the basis of the first specified area, the first comparison area being different from the first specified area; a second comparison area setting unit that sets a second comparison area within the second image; a geometric difference correction unit that corrects a difference in geometric properties between a first comparison image in the first comparison area and a second comparison image in the second comparison area; and an image output unit that outputs an image in which the second comparison image is superimposed on the first comparison image or a difference image between the first comparison image and the second comparison image, wherein the second comparison area setting unit sets the second comparison area from among a plurality of obtained second comparison areas.