oddlight

This is the Image Fulgurator, half guerrilla-art stunt and half homemade-gadget awesomeness.

Berlin based artist Julius von Bismarck uses his oddly named camera-mod to project images onto street furniture where they appear in the photos of strangers, but remain invisible to their eyes.

How?
It's simple. The device has a slave unit on top which is triggered when it sees a flash fire. This triggers his own flash, which fires through the back of the camera, through a film slide containing his slogan and then on and out through the lens at the front.

This works because a camera is pretty much a projector in reverse. And because the light-graffiti is fired at the exact same moment the unsuspecting victim takes a picture, it ends up in their photograph and paranoid mind ramblings result.