DIY mischief and then there's next level DIY mischief, and we'd have to say that Julius von Bismarck's Image Fulgurator is one of the best scare-the-squares toys we've ever come across. A sensor detects camera flashes of nearby victims, triggering a projection of the image or text of your choice onto their subjects -- and into their photos. Anyone using a digital camera will notice the trick immediately, of course, but marks with film equipment won't ever know what hit 'em -- although they might remember the weirdo with the pistol-grip camera thing standing next to them. Check the video after the break.
[Via Core 77]