Helen Evan and Heiko Hansen's Brix.

From the website:

Brix is composed of a wall of virtual bricks and a camera that sees what is happening in front of the wall. When one approaches the wall, the surface reflects the image captured by the camera, in a thousand rectangular pixels. The image of the inter-actor slips onto the wall and after a few seconds, freezes as a photograph. Brix, prefigures a new form of palimpsestual electronic architecture.

I had to look up palimpsest – it means "an object, place, or area that reflects its history".

Link (Thanks Steve!)