I have developed a way to nearly 100% block all photo enforcement systems that is legal in every state (as far as I know - I've been reading for weeks). It does not involve coating or putting anything on the license plate, or obscuring it in any manner. It is also completely invisible to the human eye - a cop following behind you would have no idea that you have any countermeasure system in place.
It is sort of complicated to have manufactured however, and I'm debating whether or not it would be worth it. I'm filing a provisional patent application shortly so I'm moving into the market research phase. After I file the patent, I can be more open to how exactly I'm doing it, but first I want to determine if I can even be profitable.
You would need one for the back of your car and one for the front if you wanted to protect both sides. It would require less work than a laser jammer to install, but about the same as hardwiring a radar detector. This is something totally different than the passive photo defense systems out there right now, and you won't even be able to get a picture of the plate from directly behind it. Also, a movie camera will not be able to get a picture of the plate either.
Basically, I want to know whether or not it's worth it to go ahead and sink money and time into developing this. It is an active electronic device, and thus would cost more than the $30-50 passive countermeasures that are out there right now. If I had to guess, I would place it in the $75-100 range (though possibly as low as $50-75) depending on several quotes from contract manufacturers I'm waiting on.
I have a working prototype built right now, but still have a couple of issues to overcome (overheating, etc). I'm pretty sure I can overcome them but just don't know if it's worth it.
Would you be interested in such a device?