The license-plate readers, which authorities typically mount along major roadways or on the backs of cruisers and government vehicles, can identify cars almost instantly and compare them against “hot lists” of vehicles that have been stolen or involved in crimes.
But the systems collect records on every license plate they encounter — whether or not they are on hot lists — meaning that time and location data are gathered in databases that can be searched by police. Some departments purge information after a few weeks, some after a few months and some never, said the report, which warns that such data could be abused by authorities and chill freedom of speech and association.
