Apparently rather old news... this article (
License Plates, Cameras, and Our Vanishing Privacy - IEEE Spectrum) points out that the Riverside County Sheriff's Dept. has been scanning since 2010. Also, it's not just the Government... repossession agencies are scanning plates too. Wouldn't be terribly surprised if the same concept was being used for some form of marketing too... park at a shopping center and soon after you start getting junk mail from the stores there...