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Last week, a firestorm of protest broke out

after it was revealed that the Department of Homeland Security was soliciting bids for a national license-plate scanner system . Using cameras with optical character recognition software networked to the motor vehicle database, these systems would allow police to track cars wherever they go. In the face of public outcry DHS has now backed off from that plan. But, given the way bureaucracy works, there's likely to be another effort, perhaps with less publicity, at some point in the future.

Local police departments in communities around the U.S. already use license plate scanners. Cameras mounted to poles or traffic signals track all the cars that pass by; cameras mounted to police cars record all the vehicles they can pick up on the road, parked alongside the road, or in driveways.

Because the cameras track the movements of people over time, without any suspicion of criminal activity, they have had privacy advocates up in arms for some time. Tracking everyone's movements over a period of weeks, months, or years allows the police to build up a detailed record of a person's habits and contacts, especially when sophisticated software correlates the movements of multiple vehicles with one another. This kind of data lets authorities know an awful lot about people, and provides an awfully tempting opportunity for abuse, such as snooping on political opponents or individuals deemed troublesome. Speak up at a city council meeting, and you might find your movements over the past few months or even years analyzed to find out who you know and whether there's anything that can be used against you.

These are not just abstract fears of abuse. As the Washington Post reports, abuse is already happening. In Washington, DC, one patrolman kept track of license plates outside a gay bar, then tried to extort the car owners. In Edmonton, Canada, the abuse was higher-level: "Edmonton officials admitted in 2005 that authorities had improperly used police computer systems to gather information on a Canadian newspaper columnist and the former head of the city's police commission, both of whom had been critics of the police department. The two became targets of a failed drunk-driving sting targeting them, according to an official review of the operation."

This stuff is bad enough at a local-government level, but at least you could move. If the federal government—already accused of abusing IRS power to stifle critics, and still reeling from the revelations of the NSA spying on citizens—were to abuse this sort of information, it would be much, much worse. That's why people were worried when news broke of a potential nationwide license plate tracking system.

But then something happened: The outcry became loud enough to cause the DHS to withdraw the bid proposal. As TechDirt's Tim Cushing wrote: "The most plausible explanation is that someone up top at the DHS or ICE suddenly realized that publicly calling for bids on a nationwide surveillance system while nationwide surveillance systems are being hotly debated was probably a horrible idea."

That's true, and the federal government's retreat in the face of pressure from its citizens is a good thing. But let's not stop there. We should not rely on public outcry to beat back this national plate-scanning idea when it inevitably resurfaces, perhaps under the cover of secrecy next time. And there's no need to wait to find out whether the courts get this issue right—or wrong.

As I noted in PopMech recently: "The Supreme Court, though, isn't the first step in protecting privacy; it's the last. If people are unhappy with the notion of having their movements, email, Web searches, and other behavior tracked, there's nothing to stop Congress, or state legislatures, from limiting this sort of activity, both on the part of private businesses and, more significantly, on the part of law enforcement. When it comes to protecting your rights and privacy, there's no reason to wait for courts to act."

If Americans want to protect their privacy, we need strong legislation that limits the kind of data the government can gather, how long they can keep it, and what they can do with it. And if I had my druthers, the law would be backed up by substantial civil and criminal penalties for violations, with civil damages to be borne by the offending officials, not the government. Fear of personal liability may be what it takes to discourage abuse.

How much privacy and freedom will Americans have in the 21st Century? The answer is the same as for previous centuries: As much as we insist on, and not a bit more.

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