When viewed through red and blue glasses an anaglyph images appears to be three-dimensional. Here's how to make a 3D anaglyph using Gimp.
You need two pictures of the same scene taken about 7cm apart. The shots should converge slightly towards the focal point of the image. Try not to use the camera's build in flash.
- first open the two images as layers in Gimp. (file / open as layers)
- select the left image (windows / dockable dialogs / layers)
- apply a red tint to the left image (colors / colorify)
- select the right image (windows / dockable dialogs / layers)
- apply a cyan tint to the right image (colors / colorify)
- select the top layer (windows / dockable dialogs / layers)
- set the top layer's mode to addition
- wear the 3D specs and if necessary adjust the layer's position
- finally, flatter the image (image / flatten image)
There are some great examples of 3D photos in Wikipedia's entry for anaglyph images. Let me know if you give this a try; I'd love to see what you create. :-)