kat them pics are great i tried to recreate a smilar one for my art piece at school i had to do it on what was like an upturned carpet as the school didnt seem to like the idea of me spraying there walls i will have a look for the pics of mine =]I love bit different, something that takes more than just skill but a sort of greater understanding, Jullian Beever is AMAZING with his 3D street art, google him but if you're too lazy the link below is a personal fave...
http://www.grand-illusions.com/images/articles/opticalillusions/beever/mainimage.jpg