The online rap sheet was impressive. There are photos of people on motorcycles without helmets, cars stopped in crosswalks, drivers on cellphones, drivers in the middle of illegal turns and improperly parked vehicles.

Using the pictures, the Delhi Traffic Police have issued 665 tickets, using the license plate numbers shown in the photos to track vehicle owners, said the city's joint commissioner of traffic, Satyendra Garg.

Despite some concerns about privacy, and the authenticity of the photos, the public's response has been overwhelmingly positive, he said.

Mr. Garg said the Facebook page never told people to take pictures of lawless drivers. “We wanted a forum where people could express their views and suggest changes,” he said Friday.

With just 5,000 traffic officers in this city of 12 million people, the social networking site is filling a useful role, he said. “Traffic police can't be present everywhere, but rules are always being broken,” Mr. Garg said. “If people want to report it, we welcome it. A violation is a violation.”

Mr. Garg acknowledged that it was possible photos could be manipulated to incriminate someone who was not actually breaking the law. But, he said, drivers can contest the tickets if they think they were wrongly issued. The police advise residents not to let personal animosity influence their photo-taking, and not to do anything to compromise their own security, like antagonizing law-breakers while snapping photos.

Some city residents have applauded the effort. “This is a good use of police resources,” said Vijyant Jain, a 27-year-old manager with Orange Business Services, who drives a minivan. He posted an alert on the Facebook page on Friday about a traffic obstruction.

A photo posted to Facebook showed a man riding a motorcycle without a helmet.

“Up until now, any driver about to break traffic laws, including me, used to look around,” Mr. Jain said, to see if there was an officer nearby before doing so. Now, drivers will be much more vigilant, he said, because “it is not only traffic cops they need to worry about.” Critics say these methods could set a dangerous precedent. Relying on people to turn in their neighbors online is “Orwellian,” said Gaurav Mishra, chief executive of 2020 Social, a social business consultancy based here. “When you start using the Internet as way for the government to keep tabs on its citizens, I start getting really worried, because you don't know where it will end,” he said. The popularity of the page shows that the ability to publicly humiliate wrongdoers “taps into a very basic primal part of who we are as human beings,” Mr. Mishra said, and it is not a pleasant one. While the Facebook page reaches thousands of people, the vast majority of residents here are not connected to it. Just one in four people in urban India has Internet access, and Internet users tend to be the wealthiest. Facebook said in July that users from India passed the 12 million mark. The authorities have embraced the Facebook informants in part because the dangers of driving in India are ever-present. India has more traffic fatalities than any country in the world, and the number of new, untrained drivers has skyrocketed in recent years as the Indian middle class grows. The system of roads and the police are ill-equipped to handle the crush. Nowhere is the problem more pronounced than in this traffic-choked city, which must contend with an additional four million more people in the metro area on top of its own population. From the beginning of the year until July 15, the police stopped 247,973 drivers who ran through city traffic signals. At the beginning of 2010, there were 6.5 million motor vehicles registered in the city, and road experts here estimate that it is adding about 1,000 motor vehicles each day. The Delhi Traffic Police now have a dedicated team of four officers who monitor the Facebook page around the clock, Mr. Garg said. In addition to examining potential violations, they also post information about closed roads and traffic jams, respond to tips about traffic snarls and answer questions. Almost 50 of the tickets issued based on photos on the site were given to police officers who were breaking traffic rules, Mr. Garg added.

Social networking services are playing a growing role in court cases and law enforcement, but the Delhi Traffic Police's use of Facebook appears to be unique.

Dozens of police departments in the United States have Facebook pages, which are often used to keep the public informed of changes in laws, warn them of dangers and solicit participants in fund-raisers.

Some departments use Facebook to connect with residents and show the human side of the force. The Houston Police Department, for example, has more than 16,600 followers, in part because of posts about the ducks that join its cadets for roll call in the mornings, and photos of recent burglary arrests taken through night-vision goggles.

On rare occasions, American police departments ask Facebook users to become involved in law enforcement. The police in Baker, LA., for instance, posted a photo on Facebook of a truck involved in a theft, asking for tips. It was unclear whether the post had led to any arrest, but one user did comment that the truck looked like one owned by a friend's brother.

In New Delhi, Mr. Garg acknowledges that there are complications to issuing tickets based on Facebook posts. People might use the site to settle scores, for example. But, he said, the response has been positive so far, and he does not want to discourage anyone from posting photos.

He also had some practical advice for Delhi's would-be citizen traffic officers. “We advise while you are driving not to take a photo” of a fellow driver who is breaking traffic laws, Mr. Garg said. Using a cellphone camera while driving “in itself is a violation.”