WASHINGTON -- If you've ever visited the nation's capital, chances are you've had your picture taken -- not necessarily by someone you know but under the watchful eye of what some consider "Big Brother."
Scores of government surveillance cameras scan images of everything from marches and protests to vehicles running a red light.
And in a new trend, more police departments are using another kind of camera -- one that scans license plates.
The license plate readers allow law enforcement officials to find stolen vehicles, a wanted or missing person, or someone on the terrorist watch list.
Each time a vehicle passes the camera, an image is collected and matched against the FBI's criminal database.
If there's a match, police can spring into action -- something they've always been able to do but not nearly as quickly or productively.
"I'm absolutely confident saying every day a felon is taken off the street as a result of this program," said Capt. Kevin Reardon of Virginia's Arlington County Police Department.
Privacy Advocates Cry Foul
For privacy advocates, the concern is what's done with the information after it's been collected.
"It's absolutely natural and justifiable to wonder about how police will without public observation use this technology," Julian Sanchez, a privacy and technology expert at the Cato Institute, told CBN News.
Sanchez says he believes it eventually could be used to reveal much more than the make, model and license plate of someone's car.
"What people, I think, ought to be pretty concerned about is the idea that everyone's movements - a map of where everyone has been -- could be stored for three years for no particular reason at all, to later then be combed through for purposes unknown," Sanchez warned.
Each of the 29 agencies in the District of Columbia area that uses the devices has a written policy on how long they store the information.
Some erase the data after a matter of days, while others keep it for a year or more. But Reardon says law-abiding citizens have nothing to worry about.
"Police officers have access to a great deal of confidential information about citizens. We safeguard that and we safeguard this information also," Reardon told CBN News.
Critics Call for More Transparency
"My heart is with the need to protect communities," American University law professor Andrew Taslitz said.
As a former prosecutor, Taslitz doesn't see a problem with using the technology. But he believes law enforcement could do a better job of calming privacy concerns by being more open about their approach between balancing safety and security against civil liberties.
"They are servants of the people, and the more that the people have a say in what they do, the more legitimate their activities are going to be," Taslitz told CBN News.
But Sanchez worries that the information could have unintended consequences.
"Most people don't expect that all of their actions in public places will be chained together and linked by any one person in ways that can reveal private facts that aren't actually exposed when you look at each public moment in isolation," Sanchez explained.
The devices are used in big and small cities across the country.
The Washington, D.C. region recently received more a $1.3 million grant from the Department of Homeland Security. A large part of that money will go toward buying more license plate readers later this year.