1. A computer-readable storage medium encoded with a computer program which, when executed by a computer, causes the computer to function as: a glare source drawing section which draws a glare source while referring to a Z value of an original image stored in a Z buffer to generate a first glare source image, and draws the glare source without referring to the Z value of the original image stored in the Z buffer to generate a second glare source image; a glare correction image generation section which performs image calculation processing including AND processing of a first image which is an image obtained by subjecting the first glare source image to first blur processing and a second image which is one of an image obtained by subjecting the second glare source image to second blur processing and the second glare source image to generate a glare correction image; and a glare expression image generation section which generates a glare expression image in which a corrected glare effect is expressed in the original image based on the original image, the blurred image of the first glare source image, and the glare correction image.