1. An image processing apparatus comprising: an image color determination unit configured to determine color of overlay image data to be superimposed on captured image data of successive frames generated by capturing surroundings of a vehicle such that a first color of overlay image data of a first frame differs from a second color of the overlay image data of a second frame following the first frame; and an image synthesizing unit configured to superimpose the overlay image data in the first color and the overlay image data in the second color respectively on predetermined positions in the captured image data of the first frame and the second frame, and output images corresponding to the captured image data of the successive frames one after another to a display.