Washington Post
By Craig Timberg

Pablo Martinez Monsivais/AP – Office Dennis Vafier of the Alexandria Police Dept., uses a laptop in his squad car to scan vehicle license plates during his patrols of the area, Tuesday, July 16, in Alexandria, Va. Local police departments across the country have amassed millions of digital records on the location and movements of every car truck with a license plate using automated scanners.

The spread of cheap, powerful cameras capable of reading license plates has allowed police to build databases on the movements of millions of Americans over months or even years, according to an American Civil Liberties Union report released Wednesday.

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.

“Using them to develop vast troves of information on where Americans travel is not an appropriate use,” said Catherine Crump, a staff lawyer at the ACLU and one of the authors of the report, “You Are Being Tracked: How License Plate Readers Are Being Used to Record Americans’ Movements.”

The use of license-plate readers is common in the Washington area, where concerns about terrorism have fueled major investments in the equipment, with much of the money coming from federal grants. Agreements among departments and jurisdictions allow sharing of the location information, with data typically retained for at least a year.