Stereogram

A 'Stereogram' is an optical illusion that creates depth in a 2D image. After some research I found a website that helps you create your own Stereogram:

http://www.eyetricks.com/stereograms/onlinetools/stereocreator.htm

I found that in order to create a stereogram you need a 3D image known as a depth map. White appears closer to the surface and black appears flat. A mask is then applied, which is made out of a repeating pattern.

Above is the depth map which should appear in the image. I'm not brilliant at it but after a while I can see it quite clearly.