1. An image projection apparatus comprising: a projection unit adapted to project an input image onto a projection surface; an obtaining unit adapted to obtain a sensed image of a range containing an image projected onto the projection surface; a generating unit adapted to generate a difference image between the sensed image and the input image; a region detection unit adapted to detect a region corresponding to an operation object for operating the image projection apparatus, based on the difference image; a position detection unit adapted to detect information relating to a position of a particular portion of the region corresponding to the operation object detected by the region detection unit; a determination unit adapted to determine an operation carried out by the operation object, based on the information relating to the position of the particular portion detected by the position detection unit; and a control unit adapted to execute an action corresponding to the operation determined by the determination unit.