An image generation system, program, and information storage medium can realistically represent reflection of light on a given object or topographic surface with a reduced computation load. The image generation system includes a section which assigns, to a given object or topographic surface disposed in a virtual three-dimensional space, a virtual object which has at least one of nonuniform brightness or color and is used for representing a light reflection effect on the object or topographic surface; a section which determines a position of the virtual object so that the virtual object moves to follow a virtual camera or player's character, and disposes the virtual object at the determined position; and a section which generates an image of the virtual three-dimensional space viewed from the virtual camera by performing translucent blending processing of the object or topographic surface and the virtual object assigned to the object or topographic surface.