In the local paper they report stories of cops pulling people over for unregistered vehicles and such using plate scanners; it seems to me that it is a way around the racial profiling issue (since the scanner picks the perps, not the “racist” cop in the car.
Very creepy stuff, but in a dying state with less and less money for cops it probably is the only way to keep revenues up.
Overview of the tech involved & privacy rights: http://www.usatoday.com/story/money/cars/2013/07/17/license-plate-scanners-aclu-privacy/2524939/