CHALK ART ILLUSIONS
IT ALL DEPENDS ON THE ANGLE
The reason it all looks 3d is because of the angle the picture was taken this was taken on a flat walkway but because of the shadowing and if you looked at one from a different angle it would appear skewed and it would look like nothing but colors.
"3D Sidewalk Chalk Artwork — Amazing Anthropomorphic Chalk Drawings Photo Gallery." Sky under the Floor. N.p., n.d. Web. 18 Mar. 2015.