1. An image processing apparatus comprising: a difference detector that detects a difference between two images according to a set detection condition; a receiving unit that receives the two images as comparison targets and a target difference image that is desirable in difference detection of the two images; and a setting unit that selects a detection condition from a plurality of predetermined detection conditions and sets the selected detection condition in the difference detector, the selected detection condition causing a difference image that is acquired by the difference detector from the two images received by the receiving unit to be closer to the target difference image.