On Tuesday, October 8, 2019, 09:17:58 AM PDT, grarpamp
The method has also drawn harsh criticism from the American Civil Liberties Union (ACLU) and privacy advocates as "a technology deployed with too few rules," and "a form of mass surveillance." There are few accurate estimates of the exact number of ALPRs across the US, which is a hodgepodge of local, state, and federal and tribal license plate readers.
I anticipated this in about 1990, although admittedly that was not much of a leap. It took longer than I anticipated to accomplish. One possible solution I thought of, in about 1996, was to cover a license plate with what 3M called "louvered film", a thin clear plastic sheet that has perpendicular black "louvers". https://www.3m.com/3M/en_US/industrial-manufacturing-us/display-enhancement-... The patent on this probably expired, so there ought to be competition in the industry. (3M's prices were always high.) A major use of this product was/is to cover the screen of a laptop (or desktop) computer, making it hard for others to see. The effect is that if you view the plate, you can't actually read it if you are looking at it at greater than a specific angle. Since many traffic surveillance cameras are mounted high up, they won't be able to see the numbers and letters on the plate. One product I just noticed, looking up the information, is: 3M™ Infrared Reflecting Film (IRF) 3M™ Infrared Reflecting Film (IRF) is a multi-layer optical film reflects > 92% of near infrared light. Color neutral, it maximizes light transmission with a natural, clear appearance. This film helps minimize thermal build-up, providing a solution for outdoor display management. Find it in ATMs, information kiosks and way-finding digital signage. Since laser radar-guns work (worked?) at about 905 nm wavelength, this product might be useful... In about 1990, I identified a PPG product, "Azurelite", (currently called "Azuria"), which absorbed all but about 6% of the single passage of a 905 nm IR pulse. So, two passages (in and out) would only allow 0.06 x 0.06 of the IR pulse to return. http://www.syracuseglass.com/E-DOCS/Architectural%20Glass/EDOCS/PPG%20Azuria... Even such a sheet might not be sufficient, however, since a license plate is made with "Scotchlite" technology https://www.3m.com/3M/en_US/scotchlite-reflective-material-us/ , which is mildly retroreflective. As a further improvement, the back surface of the Azurelite (Azuria) would be etched with hydrogen fluoride etchant (Not simply hydrofluoric acid: That merely etches smoothly; available at art stores for purposes of etching glass). This means that any IR that succeeded in passing through the glass once, would be well-scattered and illuminate the license plate over a range of angles,, and then be well-scattered yet again before being reduced by another factor of 0.06 on the way back. Two words: Stolen plates / car https://www.youtube.com/watch?v=wUG1GexVz2k