Last week at ZeroOne in San Jose, one of the art pieces reminded me of a sneaky idea I had a while ago. As you may know, many camcorders, camera phones and cheaper digital cameras respond to infrared light. You can check this out pretty easily by holding down a button on your remote control while using the preview screen on your camera. If you see a bright light, you're camera shoots in infrared.

Anyway, the idea is to find techniques, be they arrays of bright infrared LEDs, or paints that shine well in infrared but are not obvious in visible light, and create invisible graffiti that only shows up in tourist photos and videos. Imagine the tourists get home from their trip to fisherman's wharf, and the side of the building says something funny or rude that they are sure wasn't there when they filmed it.

The art piece at ZeroOne used this concept to put up a black monolith to the naked eye. If you pulled out your camera phone or digital camera, you could see words scrolling down the front. Amusing to watch people watch it. Another piece by our friends at .etoy also had people pulling out cameraphones to watch it. They displayed graphics made of giant pixels on a wall just a few feet from you. Up close, it looked like random noise. If you found a way to widen your field of view (which the screen on a camera can do) allowed you to see the big picture, and you could see the images of talking faces. (My SLR camera's 10mm lens through the optical viewfinder worked even better.)

That piece only really worked at night, though with superbright LEDs I think it could be done in the day. I don't know if there are any paints to coatings to make this work well. It would be amusing to tag the world with tags that can only be seen when you pull out your camera.