I have never heard of the spray, however I know there are liscense plate covers that blur the plate's image. The cameras that take these pictures have an extremely small shutter speed. That way, a moving car will not be blurred toobadly. The downside of this (for them it's a downside anyway) is that these liscense plate cover's spectrum is so small that even the slightest blur will be accentuated and will actually cover up the plate enough to where it can't be read in the picture. I'm not sure about this spray, but the covers work.
<span style='font-size:8pt;line-height:100%'><span style='color:blue'>1998 BMW 323is Coupe, Black
18" M3 Hyper Silver Rims
2 12" Rockford Fosgate Subs; Sealed
1.0 Farad Capacitor
800 Watt 2-Way Rockford Fosgate Amplifier</span></span>