How can that work? I've seen covers that have a retroreflective coating so if there is a flash camera the flash will be reflected directly back at the camera to overload it, but I don't know how a camera using ambient light can be blocked if a normal person can see it.
Maybe you could have the cover etched so that it is easy to see from ground level but blocked from a higher angle which cameras would have. Or maybe you could put an LCD film in the cover which blocks one side of the plate half the time and the other side the rest of the time, so in any individual frame only half the number can be seen. Run that fast enough so visually it just looks like a gray cover.
“but I don’t know how a camera using ambient light can be blocked if a normal person can see it.”
It’s polarized at an angle. An officer at ground level can see it. A camera “up high” gets a blank screen.
The law (in NM, anyway) is that it has to be visible by the naked eye 150 feet away. This, in no way, effects that.
There is also a laser emitor that you can mount by the plate that contiuoulsy generates really bright light not visible to the naked eye but that obscures the plates to cameras.
This is legal in all 50 states (while a cover is not).