I'm a bit worried that folks are confusing several different threats and their respective countermeasures, so I want to clear up a few different things that seem to be being talked about interchangeably when they really aren't. Below are numbered sections for the types of threats being discussed and the (somewhat) viable countermeasures for each.
1. Visible Light Flash Based Systems:
Traditional red light and speed camera systems. They use a visible-light camera (photo) to take a picture of the license plate of the vehicle that has committed an offense as measured by other systems (typically radar). To ensure a clear and legible photo is taken, these systems use a visible-light flash on-axis with the camera to activate the retro-reflectivity of your license plate.
1a. Retroreflective numbers/letters from the hardware store: Your license plate is retroreflective everywhere BUT the letters/numbers while these reflective numbers are retro-reflective everywhere. This means that when the flash pops and the camera takes a picture, the letters covered in tape will appear as white as the plate, as they reflect back all of the light from the flash. This is an effective and covert system for euro-plates where the backing is white and flat and can be font-matched to commercially available stickers.
1b. Retroreflective covers: these are covers or coatings that are applied over the plate to again attempt to reflect back all of the flash light, even over the numbers/letters of the plate. Varying effectiveness and obviousness with these.
1c. Flash overexposure systems: The NoPhoto is one of these, it senses the flash from the RLC or speed camera and activates it's own flash tubes which over expose the photo in the local area of the plate. These are effective, but more expensive.
1d. 3M tape: Because it somewhat reduces retroreflectivity, this may have the effect of slightly reducing contrast between the non-retroreflective letters/numbers of your plate and the retroreflective blank space on the plate. However I don't believe anyone has confirmed the efficacy of this tactic, and I wouldn't advise it.
2. IR Speed Measuring Devices (LIDAR):
This is where the 3M tape was first used. As covered previously, your plate is covered in a retroreflective coating which is superb at reflecting light back in the same direction that it impacted the plate, regardless of the angle of attack.
2a. 3M tape: was found to reduce the observed retroreflectivity of a license plate, reducing it's IR reflective signature. This was found to have some impact on the punch-through distance of older LIDAR systems. More advanced systems DO NOT need a strong retroreflector to get a strong speed reading at any distance.
2b. Veil: Similar to 3M tape, veil slightly reduces retroreflectivity but also adds an element of IR absorption to the mix. Like 3M tape this is somewhat effective, but against newer guns, unless your intent is to paint the whole car in it, effectiveness will be limited and is NOT a substitute for a good jamming system.
2b. Laser Jamming Systems: Obviously this is the preferred method to defeat LIDAR, laser Jammers fool the speed measuring device into thinking it is very close to obtaining a lock on the target by sending back pulses of IR energy that mimic the reflection the gun is expecting to see. These work very well on their own and do NOT need the assistance of 2a or 2b if installed correctly.
3. Visible light Plate Recognition Systems:
Until we have someone from the industry tell us otherwise, my assumption is that MOST ALPR systems employ visible-light video cameras to read license plates. This has been confirmed with news footage that shows ALPRs in use. The implication of a visible-light video system is that if the plate is readable to the naked eye, it is readable to the ALPR system.
3a. A plate flipper, or covering your plate in something that will physically obscure a camera's ability to read it is the only thing that will currently defeat a visible-light-based ALPR system. However this causes a problem, because in many cases the ALPR will be attached to a police car which contains a police officer who is probably curious as to why you have silly putty all over your license plate or why it's hanging from the back of your car at a 90 degree angle.
Photo of ALPR system in use: NOTE the images show COLOR not HEAT, an IR camera would not show a car as red, or white, it would show the parts of the image in various colors or tone based upon how hot they are.
View attachment 39546
4. Infrared light plate recognition systems:
Given the performance of visible light cameras, relative cost of IR cameras, and the role that ALPR is designed to fill, I'd be shocked if these are widely used. IR based systems will leverage an IR camera instead of visible light.
4a. Veil MAY reduce an IR ALPR's ability to read a plate, however this has not been confirmed. Based on tests of veil that i have seen, the plate would have to be near-black (in visible light) to be unreadable on an industrial-grade IR camera.
TLDR: NOTHING can defeat APLRs in their current state without arousing serious suspicion, however some OTHER threats can be defeated or partially defeated with plate manipulation.
I hope this helps.
