The Image Fulgurator is a device that physically manipulates photos without the photographer knowing about it.
The Image Fulgurator detects a camera flash and projects an image just for a couple of milliseconds.
The inventor called Julius von Bismarck actually won one of the prestigious Prix Ars Electronica golden Nicas this year with the Fulgurator.

On his site there is a video showing an "intervention" at the Checkpoint Charlie in Berlin. The Fulgurator is used to project a message over a sign - which is pretty puzzling to tourists.
More details on the Julius von Bismarck site. Via Heise (German).