I've seen more and more of these images popping up and I think they are simply amazing. When you look at the image from a non 3D perspective they are extremely stretched out and no exactly proportioned, thus creating such amazing and stunning images when seen or photographed from the right angle/perspective. I've tried this last summer on a smaller scale, but I failed at it...it's quite difficult and is truly something one must master or is extremely smart to figure out.
Here we have how it looks viewed correctly: Here we have it viewed from the side: And here's an article on how to create the template you'll need to create your own: How to Make 3D Sidewalk Art - Street Chalk Paintings and Murals - Forced Perspective - SideWalk Art Festivals