http://drwatson.com/tim/wallpaper.htm
This site contains a collection of ZIP files, some very large, which contain photographic images and photorealistic raytraced images. The subject matter includes scanned photographs of Stonehenge, a photograph of a brick wall, a photograph of a snow covered mountain, raytraced images of a room, and more. The images have been sized at 1024 X 768 pixels so they can be used as wallpaper in Windows, but some are also useful as background images for Web pages.