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Your license plate has been scanned repeatedly. Automatic license plate scanners have become standard equipment. They're on police cars. They're installed at intersections. And private companies use them to scan traffic, too. All this scanning has created an ocean of data about Americans' movements. And as NPR's Martin Kaste reports, police are finding new ways to use that information.
MARTIN KASTE, BYLINE: University of Washington grad student Bryce Newell has a laptop that's filled with millions of license plate scans. The scans were done by the Seattle police, and each one locates a specific car in a specific time and place, and it's all searchable.
BRYCE NEWELL: So it looks like we have a couple of hits already.
KASTE: You found me.
He plugs in my car's license, and up comes evidence of a long-forgotten errand.
NEWELL: It looks like we have you here on University Way. And this was at 3:30 in the afternoon.
KASTE: But looking up a single license plate is easy. Newell is a PhD student in surveillance - that's something you can study now. And what really interests him is what happens when you analyze millions of license plate scans at a time. He says with that many scans, you start to see larger patterns.
NEWELL: As we mix data between roving systems on these patrol cars and systems mounted on, say, red lights, the law enforcement could get a much better picture of our individual movements and, with enough data, predict where we might be or when we might leave our home or when we might be at home, for instance.
KASTE: That degree of prediction is still just theoretical. But some police agencies have started analyzing their stored plate data. Ron Sloan is director of the Colorado Bureau of Investigation. He says on one murder case his people looked at the plate scans around the area where a body was found.
RON SLOAN: We were able to do some rudimentary analysis of that data to try to determine whether or not there were vehicles that were going through the area that did not live in the area and that were from outside of the area or vehicles that that would not have been their route driving home.
KASTE: In other words, they were looking for license plates that stuck out somehow. Sloan thinks this technique is promising, and he's worried about losing it. Privacy concerns have inspired some states to limit these databases, forcing police to delete records after a period of time. Sloan is the president of the Association of State Criminal Investigative Agencies, and in March, he and other leaders of police associations sent a letter to Congress warning that the police may lose a powerful new tool because of the publics' misconceptions. That's their word. Sloan says people should remember that the police are not the same as the NSA.
SLOAN: I think it's helpful for people to understand that their fears that they're being tracked or they're somehow having their privacy violated by tracking their personal pursuits over time is not something we even have the capabilities of doing, and we have no interest in that.
KASTE: But in the end, it may not matter much that states are limiting the size of the license plate databases that police collect. That's because there's no limit on the license plate data in private hands. Jennifer Lynch is an attorney with the Electronic Frontier Foundation, and she says the nation's biggest collections of license plate data are controlled by companies such as Vigilant Solutions.
JENNIFER LYNCH: Private companies don't have the same responsibilities as government. Vigilant doesn't have to provide any transparency to the public about how it collects the data and how long it retains it for and who it shares it with.
KASTE: And there's nothing stopping these companies from letting law enforcement search their data. In fact, that's their business. The Department of Homeland Security recently announced plans to do nationwide license plate searches through a commercial service. The plan was meant to answer privacy fears about Homeland Security amassing its own giant database, but Lynch isn't reassured by that. She says it doesn't much matter to her that the license plate scans are in private hands if the government can still search them. Martin Kaste, NPR News.
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