Julius von Bismarck’s Fulgurator:

The Image Fulgurator is a device for physically manipulating photographs. It intervenes when a photo is being taken, without the photographer being able to detect anything. The manipulation is only visible on the photo afterwards. In principle, the Fulgurator can be used anywhere where there is another camera nearby that is being used with a flash. It operates via a kind of reactive flash projection that enables an image to be projected on an object exactly at the moment when someone else is photographing it.