See also optical illusions and patterns/textures.
Contributed by Jorge Iván Moreno Majul
Contributed by George Triantafyllakos
Contributed by Florian Hardwig
Contributed by Swiss Typefaces
Contributed by Edgar Walthert
Contributed by Sandoll Inc.
Contributed by Type@Cooper
Contributed by Milos Mitrovic
Photo(s) by Buro Destruct on Flickr.
Contributed by 205TF
Contributed by Marçal Prats