They are the pavement chalk drawings made by one Julian Beever, an English artist who creates crazy amazing 3-D images by employing precise distortion. It's called "anamorphic" drawing. Dad sent me another collection of his stuff the other day. There were some I hadn't seen, before, and I've seen a lot of 'em the last several years. Here's a site to visit if you want to see a whole bunch, plus, you can find others out there, as well. 
He's really come up with a performance-art home run, as he works on sidewalks or plazas all over the world, gathering big crowds. You may have seen the half-hour TV show, called "Concrete Canvas" on the GalleryHD channel (what channel?). We've seen a dozen or so of the three-day artworks in places from Amsterdam to Mexico City. It's all about the photo he takes at the end of the process (usually with himself and/or others), since the drawings, themselves are quite ephemeral and gone the same day, sometimes, due to weather or local regulations. 
He invites the onlookers to see the image through the camera lens he has set up. Otherwise, the drawing is so distorted, it's difficult to understand what it's supposed look like. He's a very engaging, low-key guy with a dry sense of humor and he's very entertaining to watch. Check it out! The images I've captured here are some of my favorites. The first one is water coming out of a hose (he's "holding" the hose). 
The second one has two humans featured: the woman on the right, and tiny Julian on the bottle cap. I love that illusion! The third is the same kind of illusion with him in the foreground and a woman atop the word, and the fourth is a drawing about the plumbing under a fountain, every bit of it drawn flat on the ground, including the fountain.I LOVE this guy! Such a way-cool idea! It's like he "sees" with an extra dimension.
