Automatic license plate readers, mounted on police cars or on objects such as road signs and bridges, use small, high-speed cameras to photograph thousands of plates every minute. The data captured by these readers (plate numbers, time stamps, locations) is collected and sometimes pooled into regional sharing systems. This information is often retained for years or even indefinitely, the ACLU reports, with few or no restrictions to protect privacy rights.

In July 2012, ACLU affiliates in 38 states and Washington DC sent public records act requests to almost 600 local and state police departments, as well as other state and federal agencies, to obtain information on how they use license plate readers. In response, 26,000 documents were sent back detailing the use of the technology around the country.

ACLU has prepared an interactive slideshow, available here, to show you what’s happening t your location information.

ACLU is calling for adopting of legislation and law enforcement agency policies adhering to the following principles:

License plate readers may be used by law enforcement agencies only to investigate hits or in other circumstances in which law enforcement agents reasonably believe the plate data is relevant to an ongoing criminal investigation.

The government must not store data about innocent people for any lengthy period – retention should be measured in days or weeks, not years.

People should be able to find out if plate data of vehicles registered to them are contained in a law enforcement agency’s database.

Law enforcement agencies should not share license plate reader data with third parties that do not follow proper retention or access principles.

Any entity using license plate readers should be required to report its usage publicly at least on an annual basis.