Photo Illusions are creative ways to confuse your mind and create false perception of things that don't exist. There are tons of funny photo illusions out there ranging from exploiting false perspective (eg. catching sun in hands during sunset, holding the tower of Pisa etc.) to paintings on walls making the impression that there is no wall but rather we see what is inside the building.
The mentioned paintings are actually called "trompe l'oeil", which comes from French and means "deceive the eye". You might have seen such murals fooling us into seeing 3D scenes which are painted on a regular flat wall. It's funny how we like to be tricked.