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License plate scanning: The inside story of a cop who tracks our data

Mark Sullivan | July 23, 2013
We talk to an Oakland, California stolen car investigator about how license plate scans are used to solve crimes.

London calling
Mass license plate scanning got its start in London during the 80s and 90s as a way of keeping track of terrorists from the time they entered city limits to the time they left. Law enforcement around the world quickly saw the appeal of this, and adopted the technology to hunt down stolen vehicles. By 2002, police in the United States were routinely using the technology, Hinch says.

After 9/11, police departments nationwide suddenly had access to a lot more federal funding for all kinds of surveillance gear, several sources told TechHive. Some of that money came from the Department of Homeland Security, and has been used by police departments small and large to buy license plate scanning gear.

As plate scanning technology matured, it became a stand-out tool for chasing bad guys. "They have really ramped up the number of cameras in the last few years. And they're using longer retention times for the data," says Electronic Freedom Foundation staff attorney Jennifer Lynch.

The cameras mounted on police cruisers can scan up to 2,000 license plates a minute, and immediately store the image in the cloud, according to Tripwire security researcher Ken Westin, who routinely works with law enforcement agencies to solve crimes.

And the plate scans yield more than just a series of numbers. The images can include a large portion of a car surrounding the plate, including any identifying marks (dings, stickers, etc.), as well a GPS tag of the exact location of the scan, and a time stamp. All this information can be sent back to a database in milliseconds, Westin says.

With all this data in hand, police can investigate a much larger set of crimes, like burglaries, sexual assaults, child abductions, and even domestic abuse cases, Hinch says.

Because the cameras are constantly scanning, the same vehicles in a given jurisdiction show up over and over again. When these scans are plotted on a map, individual license plate numbers can begin showing up in clusters over time—and some of these locations can be crime scenes.

For example: Let's say the police know the addresses of four burglaries, and the details of each crime indicate a pattern—a common perpetrator. The police can search the database of all plate scans in the vicinity of those crimes, and pull up any vehicles that were present at more than one of the locations at the times the crimes were committed. The owners of these vehicles, then, become serious leads.

Bad for criminals, but at what cost freedom?
It all sounds like a perfectly wonderful law enforcement tool, but the vast majority of plates being scanned are owned by innocent, law-abiding people. The ACLU study shows that less than one percent of the plates scanned are owned by criminals.


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