2017-12-23:
Autostereograms
Autostereograms are single-image stereograms, intended to create a 3D illusion if looked at properly - the viewers need to relax their eyes and focus on a point behind the image, until two similar parts of the pattern merge together. Most people can learn how to do it. The effect works because of tiny offsets in the pattern over the horizontal axis, resulting in the illusion of depth in the brain.
Advanced
Interactive