1. A computer-readable storage medium having stored thereon an image processing program to be executed by a computer of an image processing apparatus that displays an image on a display device, the image processing program causing the computer to function as: captured image acquisition means for acquiring a captured image captured by a real camera; virtual world image generation means for, using as a texture of an object to be placed in a virtual world an image included in a predetermined area in the captured image acquired by the captured image acquisition means, generating a virtual world image in which the object placed in the virtual world is viewed from a virtual camera; image combination means for combining the captured image acquired by the captured image acquisition means with the virtual world image; and display control means for displaying the image combined by the image combination means on the display device.