As the investigation of the Boston Marathon bombings illustrates, getting lost in the crowd is no longer an easy feat. There are eyes -- and cameras -- everywhere.
Investigators swiftly obtained a vast quantity of amateur photos and videos taken by onlookers as well as extensive footage from surveillance cameras in the area of the blasts. The FBI released images Thursday from one of those cameras, zeroing in on two men who proved to be the suspects in the case.
One of the men was killed overnight in a gun battle with police; his brother was captured by Boston police Friday evening.
With the crucial role played by video in the Boston case, surveillance cameras -- which have proliferated in London, Chicago and elsewhere -- may take on new allure.
Informal surveillance by private citizens may proliferate as well; the FBI says it expects the public to be its "eyes and ears." The upside of this expanding surveillance network is clear -- a greater potential for law enforcement to solve crimes and, in some instances, to prevent them.
While some civil libertarians welcome any tools that can help solve a crime, they also worry about an irrevocable loss of privacy for anyone venturing into public places.
"It's now harder and harder to go about our lives without being tracked everywhere," said Ben Wizner, a lawyer with the American Civil Liberties Union who specializes in privacy and technology issues.
"The ACLU doesn't object to cameras at high-profile public places that are potential terrorist targets," he said. "What we do object to is a society in which cameras are so pervasive that we can't go about our lives anywhere without them being recorded and stored in databases forever."
Within the past decade, the scope of surveillance -- both private and government -- has increased incalculably. Just this week, security video helped lead to the arrests of a Texas couple in the slayings of two prosecutors and the wife of one of them.
Authorities say the accused man, a former justice of the peace, was embittered because he had been convicted of stealing government computer monitors -- an offense that was itself captured on security video.
And then there is self-surveillance. Millions of people check in regularly with Foursquare to communicate their whereabouts; many millions more passively enable themselves to be tracked simply by carrying their cellphones.
Photographs and videos can rocket through cyberspace, instantly viewable by strangers on the other side of the world or by law enforcement agencies, courtesy of Instagram, Facebook, Twitter and other social media.
Attitudes toward surveillance and privacy may be shifting. There's a generation of teens and young adults who have grown up with social media and may be more reconciled than older Americans to the prospects of being tracked.
"Americans still cite privacy as one of the core values they cherish, but what's happening is this slow, insidious erosion of it," said Jonathan Turley, a law professor at George Washington University. "And yet we have a generation being raised in a fishbowl society. They're more tolerant of government surveillance, and that can be a danger to a free society."
Compared to the United States, surveillance cameras are far more pervasive in Britain, where they were first used decades ago to protect against attacks from Irish militants. Up to 4 million or so cameras are now in place, including some around the house of George Orwell, the author of "1984," which foretold of a "Big Brother" society.
Among the British public, the cameras seem to be widely accepted, especially after the 2005 suicide bombings that killed 52 people during morning rush-hour traffic in London. Evidence from closed-circuit cameras helped crack the case.
Nonetheless, a London-based group called Big Brother Watch has been campaigning to cut back on the surveillance network.
"While it provides a sometimes useful tool after an event, it doesn't address the root causes of crime and doesn't protect the public," said the group's director, Nick Pickles.
In the United States, Chicago has the largest network of surveillance cameras, estimated at more than 10,000. They are mounted on street poles and skyscrapers, aboard buses and in train tunnels; the rail system alone has more than 3,600 cameras.
Police credit the network for thousands of arrests in recent years. Cameras have recorded drug deals, bike thefts and other crimes; footage from a camera on a city bus helped convince a suspected gang member to plead guilty to shooting a high school student in 2007.
After the Boston Marathon bombings, Mayor Rahm Emanuel was quick to tout Chicago's surveillance cameras.
"They serve an important function for the city in providing the type of safety on a day-to-day basis -- not just for big events like a marathon," he said.