With the rapid growth of “security” cameras, I’ve seen a number of articles discussing how to avoid them. This could go from something simple, like wearing a long-brimed baseball cap, to using lasers to wipe out the image. One of the more interesting techniques is to use powerful IR sources.
IR refers to the infrared area of the spectrum, lying outside the range of human sight. It’s light, but we can’t see it. The most common use of IR is your TV Remote Control. It flashes a sequence which is interpretated by the receiving unit (your TV). Since it’s light, it’s a line of sight technology (i.e. it can’t go through opaque objects, like walls or your hand).
The key is that most video cameras are very sensitive to IR (unless they are filtered). This allows for sensitive night vision capabilities without having any visible light source. The “night mode” on your camcorder is an example of how the camera uses IR, often with an IR light source to light the subject being filmed, without the subject seeing it. The conversion from IR to visible is done in shades of green, which is why nightvision stuff typically looks green.
This sensitivity to IR is used by jammers to wash out the picture. For example, if you point your camcorder to a bright light source you’ll notice that the picture gets washed out (at least until the auto-exposure takes over). Here’s an example:

In the above photo, the person has attached a strong IR source (a bunch of IR LEDs) to a baseball cap. This IR light floods the camera, turning their head into a bright white orb.
Obviously, this makes you stand out in a crowd, but it also means that you can’t be identified. And, if everyone dons this electronic version of a Guy Fawkes mask, then there will be nothing but bright blobs walking around. In fact, this technique has already been used during bank robberies, effectively making the security cameras useless.
The downside is that this will only work on cameras without an IR filter. If they are properly filtered, then they will probably not be affected. However, low-light / night cameras will almost always use IR, and be highly sensitive to it, so jamming under night conditions is almost guaranteed to work.
While being able to jam Big Brother is interesting, I thought of something more fun to do with this concept. For example, you could rig a baseball cap with IR LEDs and have it display a big light-up middle finger. Those around you would see nothing, but those security cam watchers would see a big F-U on their screens. You could even go one step futher and walk around with one of these:

What you see above is called “Peggy” by Evil Mad Science. It’s sort of an LED Lite-Bright, if you will. What I would do is this: Put a nice smily face design on there, in visible yellow LEDs. Then, interlaced with the visible yellow, I’d put a message made from IR LEDs. In effect, you’d have an invisible (to the human eye) message hidden in a pleasant visible icon.
I can see it now! The furious security camera guy seeing “Fuck You” on his screen and sending down the Gestapo to question you. When the Gestapo arrives, all they see is a smiley face. That would keep them guessing. You could protest security cameras without offending your neighbors.
For those who dislike the Google StreetView as much as I do, you could take one of these and make an IR sign for your living room window. Perhaps a big Mind Your Own Business or something more crude. Since it would be in IR, only the Google cameras would see it, so you can be vulgar without your neighbors knowing it (unless, of course, they point a camcorder at your house–in which case, they get what they deserve!).
This idea could also be used as a novelty. For example, you could have a hat that subtly “paints” your face in IR. So, if someone takes a camera phone photo of you, they get a picture of a goulish looking person. Perhaps you could even rig up some soft of IR halo. You’ll be the hit at parties.