The Saint Paul Police Department (SPPD) recently increased the length of time that it retains scans of vehicle license plates from fourteen to ninety days.
Many municipal police departments are now employing LPR (license plate recognition) technology to capture thousands of license plate images on a daily basis. In Minnesota, these images are cross-referenced against a database maintained by the Bureau of Criminal Apprehension, which also contains stolen vehicle and wanted person data from the FBI. Matches result in alerts that are intended to focus additional officer scrutiny on particular vehicles, in order to check for stolen property, warrants, and related matters. The system also records GPS data correlated to the location of the license plate at the time of the scan.
The SPPD manual notes that “LPR data is maintained for a short time on the LPR hard drive.” Afterwards, unit commanders are responsible for seeing that LPR scans are maintained for a “minimum of 90 days” at which time they are no longer maintained, unless specific LPR data results in an arrest for an offense. In those cases, the data is retained according to another SPPD retention schedule.
The pervasive scope of LPR systems, the length of the retention of the data, and the ability to aggregate the data to provide detailed pictures of the movements of individuals have raised questions and controversies about the use of LPR technology.