1. A non-transitory 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 unit acquiring a captured image captured by a real camera; virtual world image generation unit, 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 unit, generating a virtual world image in which the object placed in the virtual world is viewed from a virtual camera, wherein the virtual world image generation changes a direction of viewing from the virtual camera the texture of the object to be placed in the virtual world in accordance with a direction of the virtual camera relative to the object; image combination unit combining the captured image acquired by the captured image acquisition unit with the virtual world image; and display control unit for displaying the image combined by the image combination unit on the display device.