Inventors in Scottsdale, Arizona are hoping their device intended to defeat red light cameras and speed cameras catches on. The "Photo Fin" is a reflective, stainless steel device that looks like a shark's fin mounted perpendicular to the surface of the license plate. From a ten degree angle, at least one letter of the license plate is physically blocked from view, meaning cameras mounted on the side of the road should be unable to read the plate.

"The Photo Fin alters what a photo radar camera 'sees' and as a result cannot issue a citation, thereby leaving the enforcement to the true professionals -- trained, intelligent, reasoning human officers, capable of making decisions regarding reasonable and prudent operation, traffic flow and volume, road conditions, weather, potential hazards and safety," the Photo Fin website explains.

A number of other license plate blocking products, including sprays and plate covers, often produce mixed results. Sprays and reflective covers are also ineffective against newer ticket cameras that use infrared and video technology instead of flashes. In March, the Discovery Channel's MythBusters television program showed several types of plate covers failed to defeat the cameras operated by ATS, a Scottsdale camera vendor.

While the Photo Fin appears to solve many of the limitations of previous plate blocking techniques, it remains to be seen how police officers and the court will respond to motorists driving with obvious objects tacked onto their license plates. The device also does not prevent camera vendors from using computer algorithms to guess what the missing plate number might be. Dozens of motorists have been wrongly ticketed when the guess turned out to be wrong.