The image below looks like an orange design is superimposed on a photo, right?
Actually, the orange design is superimposed on the real world. It is painted on the left alley wall, the right alley wall, and the parking garage further away. The three parts do not touch, but from the end of the alley where the photo was taken—off Chapel Street between College and Temple in New Haven, CT—the parts form a convincing whole.
For the full effect of walking down the alley, this article has a video (highly recommended), plus additional background about the piece, Square with Four Circles by Felice Varini. He just finished it this past week. It will be up until 2011.
Thanks to Greg and Nina for pointing it out as we passed by.