It's a scenario out of a sci-fi movie: a surveillance camera that records your face, transmits the image to a database, and raises an alarm if you're a suspected terrorist, a sex offender, or a missing person.
But what if you're an Al Qaeda agent in a Groucho Marx mask?
Then it gets a little more complicated, as police in Tampa, Fla., discovered a few years ago when surveillance camera technology was a security trend. Under the FaceIt scanning program, the police scanned 100,000 unknowing fans at Raymond James Stadium during the 2001 Super Bowl. But the project was ultimately shelved, in 2003, partly because antisurveillance activists discovered the cameras could be fooled by ski masks, bandannas, even sunglasses.
Interest in the technology never wholly faded, and now, in the wake of the London attacks and the widely publicized use of cameras to track down suspects in those incidents, some politicians in the United States are again saying it's time to seriously consider increased video surveillance. Although they eschew Tampa's complicated biometric bells and whistles in favor of simpler recording networks, the cameras are going up in New York, Baltimore, New Orleans, Chicago, and Detroit: in subway tunnels, at bus stops, on downtown promenades, and in low-income neighborhoods. With the programs comes a lively debate on security versus privacy, cost versus effectiveness, and the role of the government when it comes to protecting - and monitoring - citizens.
"People feel safer if they know an area is being watched," says Vincent Morris, a spokesman for Washington Mayor Anthony Williams, who has publicly stated his support for increasing public surveillance since the 7/7 attacks. Mr. Morris calls the cameras a necessity in a city that has already been a terrorist target and describes them as more of a deterrent than an outright preventive measure: "We've had red-light cameras here, and they cause people to slow down," he says.
Some cities are moving ahead quickly. A week after 7/7, New York announced that its Metropolitan Transit Authority would begin installing cameras in the underwater tunnels that link Manhattan to outside neighborhoods.
All of this raises the issue: Cameras that discourage drivers from running red lights are one thing. But suicide bombers, experts say, are liable to blow themselves up whether they're being recorded or not.
Still, in their investigations after 7/7 and the attempted 7/21 attacks, British law enforcement has made extensive use of surveillance tape.
"[Cameras] have huge post-incident investigation value and potential prosecution value. One of the reasons the London authorities have made the progress that they've made is because of the images they had on the camera," says Jack Riley, a crime and security expert at the RAND Corp. in Pittsburgh.
But such use alone does not make a city secure, he adds.
"I would put cameras in the same category as improved lighting, increased foot patrols, and the use of explosive-detecting dogs - as a potential deterrent."
Some civil liberties activists agree with that assessment. But they also see huge potential for abuse: a looming threat of privacy invasion and hints of a Big Brother-esque state where all public activity is recorded and analyzed.
After all, surveillance doesn't just happen in subway stations. In June 2004, the libertarian Reason magazine, using public databases, sent some 45,000 subscribers a personalized issue with a satellite image of their residence on the cover.
"We had some people cancel their subscriptions after that," says Reason editor Nick Gillespie. Ironically, the issue addressed the "upside of zero privacy" - such as ease of marketing - but that said, Mr. Gillespie doesn't shirk from criticizing a watchdog society.
While he acknowledges that footage helped the London investigations, he makes it clear: "I don't necessarily think that tells us surveillance of public areas is an unfettered good thing."
He adds, "There are TV shows in England that show outtakes from surveillance cameras. There's something weird about that. There's something creepy about that. We fundamentally have to ask ourselves, are we an open society or not?"
The European Parliament addressed such a question, in the 1998 report "An Appraisal of Technologies of Political Control." Europe in general, and the United Kingdom in particular, makes heavy use of surveillance technology in public places, and the report warned against monitoring abuses that smack of totalitarian regimes.
In a section titled "Developments in Surveillance Technology," the report reads, "Much of this technology is used to track the activities of dissidents, human rights activists, journalists, student leaders, minorities, trade union leaders and political opponents."
But if abuses occur in the US, they'll occur under the auspices of a transparent system where citizens can hold authorities accountable, argues Robert Atkinson, vice president of the Progressive Policy Institute in Washington.
Mr. Atkinson says that surveillance systems, like any tool - especially law-enforcement tools like guns - can be potentially abused. But he adds that in a cost-benefit analysis, they are a cheap, efficient way to keep tabs on public spaces, which is a police officer's duty anyway.
"Put it this way: If we had the money, we could put a cop in every station," he says. "How is that different from a video surveillance system?"
Some say it is. They argue that the cameras are too impersonal yet simultaneously too intrusive. But critics and proponents agree that the issue is not really a question of equipment. It's the policy associated with the technology.
There is "a very thorny issue on what your policies and procedures are going to be when it comes to monitoring," says Mr Riley of RAND. "If departments are smart, they're going to get out in front of this, because sooner or later they're behind it, and that's not a good place to be if you're making policy."