In Alexandria City (and, I suspect, in some other Virginia jurisdictions), several police cars are equipped with cameras that automatically capture license plate images which are then automatically checked against a database of stolen vehicles and if there's a hit, the officer is notified. I don't know if there are other databases against which the plate is checked, e.g., registered to a person with a warrant. There was some recent controversy in Alexandria City as to how long the plate images are stored. If they are stored for ANY length of time, IMO, then they are building a "who was where" database that could be used to track citizens, which seems counter to the original purpose.