You Are Being Watched: License Plate Readers & The End Of Privacy

October 1, 2012

Most of us are familiar with traffic cameras that monitor roadways for speeders and red-light runners. But how much do you know about licence plate readers, or LPRs?

Ars Technica has posted one of the most thorough and thoughtful examinations of LPRs to date, and the implications for drivers are fairly staggering. If you're the sort of person who gets antsy at the mention of Big Brother, you might want to skip to another article, because modern technology is making privacy a thing of the past.


Technically speaking, LPRs aren't all that different than other traffic cameras. Look across the U.S., and you'll find tens of thousands of them attached to street lights, next to traffic signals -- even mounted on moving vehicles.

The software they use is similar, too. Like red-light cams, LPRs take photos of plates, then scan those images to identify license numbers.

The difference is in how data gathered by LPRs gets used.

Red-light cameras, for example, are trained on intersections. Though they film every vehicle that passes by, they often dump that information if a vehicle behaves lawfully. When a car runs a light, however, the data is retained, and the plate is scanned. The images are often reviewed by a human -- frequently, someone hired by the for-profit company that installed the camera system -- and if the driver has, in fact, broken the law, a ticket is dropped in the mail.

LPRs, on the other hand, retain their data for months, years, or in some cases, indefinitely. Scanned plates are matched against databases of stolen cars or vehicles owned by criminals, which can take some time. And even then -- even if a vehicle is found to be in the clear -- the data is sometimes kept on file.


LPRs are a problem that few people saw coming. In a way, they're a bit like autonomous vehicles. Google, for example, wasn't technically breaking any laws by testing its self-driving cars in California, because the state doesn't stipulate that vehicles have to have human drivers. Who would've ever thought that such a thing would need to be written down?

Similarly, not many people -- other than, say, science fiction writers -- could've envisioned a day when license plates were tracked on streets, in malls, and on college campuses across the nation. Now, the legal system is having to play catch up. Here are a few of the problems that city, state, and other officials will have to address in the near future:

  • Ownership of license-plate data: Some LPR companies sell camera and systems to cities, counties, and states, which then create their own databases of scanned plates. Those databases are government property. Other LPR companies practically give away their hardware so that they can develop massive troves of plate data themselves. Few rules govern how that data can be used, with whom it can be shared, or to whom it can be sold.
  • Standards for data retention: At the moment, there's no national standard for how long LPR systems should hold on to data. Scanning for stolen vehicles happens fairly quickly -- often within a matter of minutes or hours. But what if someone's condo is burglarized while they're away on vacation? Having access to a few weeks' worth of plates from a parking garage could help identify the culprit. Public officials seem to want to limit data retention to a few months, but the companies that maintain their own license-plate databases obviously want to keep their files much longer. After all, more data means more value, and more value means more revenue.
  • Interfacing with multiple databases: All these databases floating around are formatted in slightly different ways. So even when files from one agency should be able to "talk" to files from another agency, they may not be able to do so. For example, if a stolen vehicle's license plate is found in a state database, but a particular city's LPR system isn't built to interact with the state database, it won't see the stolen vehicle when it passes through. That's a fail.
  • Alerting the public: Many states and cities have laws requiring that notices be posted wherever traffic cameras are in use. There seem to be few, if any, such laws for LPRs.


It's hard to argue against LPRs when they're being used to fight big crimes like auto theft, kidnapping, and terrorism. However, it's also possible to use LPRs to catch low-level crimes, like parking violations. 

That's because the law is currently on the side of LPR operators. While you might expect that the contents of your vehicle are your own and should remain private, that privacy doesn't extend to your license plate. In fact, in the case of United States vs. Ellison, an appellate court found that "a motorist has no reasonable expectation of privacy in the information contained on his license plate under the Fourth Amendment". (The Fourth Amendment is the one that protects citizens from unreasonable searches and seizures.)

In the best of all possible worlds, the government would establish standards for LPRs and similar monitoring systems to protect individual privacy. Our inclination is to have such standards set at the federal level, so there's a degree of consistency from state to state.

That's important not only for drivers, but also for non-drivers. Before long, facial recognition cameras will be as widely deployed as LPRs, so issues like these -- issues around technology and privacy -- ought to be resolved sooner rather than later.

Are you comfortable with LPRs, or do they give you the willies? Drop us a line, or leave a note in the comments below.

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