Unfortunately they can as long as they have a legal right to be where they were when they spotted your plates. This frequently happens when a police officer is behind someone at a traffic light. The courts have reasoned that sense license plates are in full view therefore there are no privacy concerns. I and many of my fellow constitutionally minded attorneys disagree but that is the law. Many cities and towns now are even investing in automatic license plate readers which are machines that will automatically scan license plates in parking lots to check for expired tags, invalid drivers license, and warrants.
Answered on Apr 02nd, 2014 at 6:35 PM