The American Civil Liberties Union is warning that law enforcement officials are using license plate scanners to amass massive and unregulated databases that can be used to track law-abiding citizens as their go about their daily lives. In a new report, "You Are Being Tracked: How License Plate Readers Are Being Used to Record Americans' Movements," the ACLU discusses the data culled from license plate scanners - cameras mounted on patrol cars, overpasses and elsewhere to record your license plate number and location at a given time. There are tens of thousands such cameras now in operation, according to the group, with the data in some cases being stored indefinitely. The ACLU report is the result of an analysis of 26,000 pages of documents from police departments around the country, obtained through nearly 600 [FOIA] requests. It finds that while some jurisdictions keep the information gleaned from the scanners for a short time ... many hold onto the data for years. The organization complains that there are "virtually no rules in place" to keep officials from tracking "everybody all the time." The ACLU also warns that the data is being fed into larger databases, with the private National Vehicle Location Service now holding more than 800 million license plate records. The group's database is used by more than 2,200 law enforcement customers. The [ACLU] report warns that the data can be used in an official capacity to spy on protesters or target communities based on their religious beliefs, or unofficially by a police officer who wants to keep an eye on a romantic rival.