1. An image composition apparatus comprising: a parallax deriving unit configured to derive parallax of one area in a background image, the one area corresponding to one object in the background image; an image selection unit configured to select an image which has a parallax different from the parallax of the one area in the background image, as a material image, from a plurality of three-dimensional images, each of which is viewed as a specific object in a three-dimensional manner; and an image composition unit configured to superpose the material image selected by the image selection unit on the background image.