An autostereogram is a single-image stereogram (SIS), designed to create the visual illusion of a three-dimensional (3D) scene from a two-dimensional image. In order to perceive 3D shapes in these autostereograms, one must overcome the normally automatic coordination between accommodation (focus) and horizontal vergence (angle of one's eyes). (Wikipedia)
The brain is surprisingly capable of instantly matching hundreds of pattern repeated at different intervals in order to recreate correct depth information for each pattern. This autostereogram contains some 50 tigers of varying size, repeated at different intervals. Despite the apparent chaotic arrangement of patterns, the brain is able to place every tiger icon at its proper depth.
This is an Object Array Stereogram (a type of autostereogram) of a chessboard with some chess figures. If viewed with parallel method a stereoscopic relief will appear.
If you have difficulty in seeing the 3D image, cross eyes slightly until a third white dot appears between two. Now your eyes are in a 3D mode.
a This autostereogram features a raised shark with fine gradient on a flat background.The shark figure in this depth map is drawn with a smooth gradient. If you have difficulty in seeing the shark, cross eyes slightly until a third white dot appears between two. Now your eyes are in a 3D mode.
If you still have difficulty in seeing the shark, the following animation picture is easier for you to unfocus.
Instructions: Hold your thumb close to the center of the image, and then focus on your thumbnail tip. Then while maintaining focus on your thumbnail tip slowly bring your thumb closer to your eyes until the shark outline shows up. Repeat as necessary until you see the shark outline.