An anonymous reader quotes a report from The Register: Police departments cannot categorically deny access to data collected through automated license plate readers, California's Supreme Court said on Thursday -- a ruling that may help privacy advocates monitor government data practices. The ACLU Foundation of Southern California and the Electronic Frontier Foundation sought to obtain some of this data in 2012 from the Los Angeles Police Department and Sheriff's Department, but the agencies refused, on the basis that investigatory data is exempt from disclosure laws. So the following year, the two advocacy groups sued, hoping to understand more about how this data hoard is handled. The LAPD, according to court documents, collects data from 1.2 million vehicles per week and retains that data for five years. The LASD captures data from 1.7 to 1.8 million vehicles per week, which it retains for two years. The ACLU contends [PDF] that indiscriminate license plate data harvesting presents a risk to civil liberties and privacy. It argues that constant monitoring has the potential to chill rights of free speech and association and that databases of license plate numbers invite institutional abuse, not to mention security risks.