Law enforcement officials, and amateur sleuths, cross-referenced photos of the Boston Marathon finish line with massive databases of other pictures in an attempt to name the bomber. (The Fold/The Washington Post)

Five days of harrowing footage from Boston has allowed a voracious nation to experience Monday’s bombings and their aftermath almost as the events were happening, with ever-present cameras at once documenting history and pushing it relentlessly forward.

Fueling this situation has been a series of technological shifts that are likely to accelerate in the years ahead as police, corporations and even private citizens gain access to unprecedented troves of video imagery and the tools to analyze them.

Advances in computing power and analytical software have allowed for individuals to be identified and tracked as never before — especially when that information is combined with the location data emitted by most cellphones.

The role of these technologies in the Boston investigation is unclear, but law enforcement experts say that video surveillance and analysis is especially valuable in cases such as this, with an unexpected attack and no obvious suspects at first. The process of winnowing happened with remarkable speed, moving in just days from a mountain of unsorted video, to blurry images of potential suspects, to pictures crisp enough to drive a manhunt.

For those seeking to protect privacy in the digital age, however, the news is not all good. Computer analysis of the faces of those who apply for driver’s licenses, passports or entry visas already has created vast databases that some law enforcement officials are eager to use on a routine basis, for what amounts to digitized lineups of tens of millions of people.

The debate over how to balance the needs of investigators with the rights of private citizens remains unsettled. Civil libertarians worry that data gathered for one investigation will inevitably be used for other purposes, allowing a gradual slide into perpetual surveillance of private citizens.

There are so many video cameras operated by so many entities, public and private, that no one has a credible count of how many are in use, though estimates in lower Manhattan alone top 3,000, said Jennifer Lynch, a staff attorney with the Electronic Frontier Foundation.

“Somebody who lives and works in that area could be surveilled in almost everything they do,” she said. “That is a society that most of us do not want to live in.”

Analyzing video has been key to bombing investigations worldwide and was especially key to unraveling the Islamist bombings in July 2005 in London, perhaps the city with the world’s most extensive network of video surveillance.

Cameras were key even as long ago as April 1999, when a bomb injured dozens of people at a market in Brixton, a district in south London, said Hugh Orde, a top police official during the investigation.

“We had, from a detective point of view, a disaster,” he recalled.

But by reviewing surveillance videos, police identified a man wearing a cap low on his head and carrying a bag. In another clip, the bag was gone. The pictures broke open the case and led to an arrest.

Facial-recognition technology used by the FBI was first developed during the Iraq War to search for suspects in the aftermath of bombings, which typically featured crude, handmade explosives resembling those used in Boston.

“This is eerily similar to Iraq,” said James Albers, senior vice president for government operations for MorphoTrust USA, based in Billerica, Mass., which makes facial recognition software for the FBI. Its development is part of a $1 billion push for a new generation of technology that eventually will include recognition of a person’s irises and palm prints as well as traditional fingerprints.

Facebook and Google also have extensive facial-recognition data, gathered when users upload photos. Police typically need a search warrant for a particular suspect in order to access that information.

The facial-recognition software used by the FBI can lift shadows, sharpen blurry pictures and create three-dimensional images from flat ones, Albers said. It also analyzes each face to develop a unique “template” based on the shape, skin texture and distances among features.

Still, facial-recognition software remains imperfect. In most cases, the human brain is more adept at identifying individual faces, experts say. Computers are most valuable when seeking to compare an image with many possible matches, such as in a database.

The FBI, which declined to comment about the use of such technology in the Boston case, ultimately turned to the public in its quest to identify two key bombing suspects, even though it later turned out that one of them had a driver’s license photo on file in Massachusetts — one of at least 30 states that use facial-recognition software to analyze its database of motorists.

Though the software is used mainly to detect fraud when people get more than one driver’s license, the rate of false positives remains high. Claims about precision often are overblown, say those who study the technology.

“The public has grown up in a world of ‘CSI Miami,’ ” said Marc Rotenberg, executive director of the Electronic Privacy Information Center. “The real world is much more complicated.”

In one case of mistaken identity in 2011, covered at the time by the Boston Globe, a suburban Boston man received a letter from the state Registry of Motor Vehicles telling him that his license had been suspended.

Only after he hired an attorney and missed more than a week from his job as a truck driver did officials explain that a facial-recognition program had concluded that he and the holder of another license were the same man. The error was corrected and the man’s license reinstated after a contentious hearing and the filing of new identity documents.

“It was a really nasty, unpleasant experience all around,” said the man’s attorney, William Spallina.

Whatever limitations exist in the software are likely to be surmounted in the next several years. Engineers are working to improve the clarity of images and the ability of software to recognize abnormal behavior before an incident occurs. A future generation of analytical software might, for example, identify a man putting down a backpack at a busy event and immediately alert police.

“There are certain situations when you give up some of your privacy, and we’ll be seeing that more and more,” said Albers. “The old idea of privacy . . . certainly is changing.”

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