1. A system for compressing a motion picture generated by projecting objects onto a screen, the objects moving relatively to the screen in a three-dimensional (3D) space, the system comprising: a motion calculating component which calculates a motion vector of the object within the screen by projecting onto the screen a motion of the object in the 3D space between a time corresponding to a frame to be compressed (hereinafter, referred to as a compression target frame) and a time corresponding to another frame; and a compressing component which compresses the compression target frame by motion compensation based on the motion vector.