By BRIAN STELTER and BRAD STONE


AT ONE TIME, authoritarian regimes could draw a shroud around the events in their countries by simply snipping the longdistance phone lines and restricting a few foreigners. But in the 21st century, cellphone cameras, Twitter accounts and all the trappings of the World Wide Web have changed the ancient calculus of how much power governments actually have to sequester their nations from the eyes of the world and make it difficult for their own people to gather, dissent and rebel.

Iran’s sometimes faltering attempts to come to grips with this new reality are providing a laboratory for what can and cannot be done in this new media age. It is also providing lessons to other governments about what they may be able to get away with should their own citizens take to the streets.

One early lesson is that it is easier for Iranian authorities to limit images and information within their own country than it is to stop them from spreading rapidly to the outside world. While Iran has severely restricted Internet access, a loose worldwide network of sympathizers has risen up to help keep activists and spontaneous filmmakers connected.

Shortly after Neda Agha-Soltan bled her life out on the Tehran pavement on June 20, a 40-second video of her death ricocheted around the world. The man who shot the video e-mailed the twomegabyte file to a nearby friend. Evading government censors, he quickly forwarded it to the Voice of America, The Guardian and five online friends in Europe, with a message that read, “Please let the world know.”

Copies of the video, as well as a shorter one shot by another witness, spread almost instantly to YouTube and were televised within hours by CNN. Ms. Agha-Soltan was transformed on the Web from a nameless victim into an icon of the Iranian protest movement.

The pervasiveness of the Web makes censorship “a much more complicated job,” said John Palfrey, a co-director of Harvard’s Berkman Center for Internet and Society.

The Berkman Center estimates that about three dozen governments - as widely disparate as China, Cuba and Uzbekistan - extensively control their citizens’ access to the Internet. Of those, Iran is one of the most aggressive. Mr. Palfrey said the trend has been toward more, not less, censorship. “It’s almost impossible for the censor to win in an Internet world, but they’re putting up a good fight, he said.

Since the advent of the digital age, governments and rebels have dueled over attempts to censor communications. Text messaging was used to rally supporters in a popular political uprising in Ukraine in 2004 and to threaten activists in Belarus in 2006. When Myanmar sought to silence demonstrators in 2007, it switched off the country’s Internet network for six weeks. In early June, China blocked sites like YouTube to coincide with the 20th anniversary of the Tiananmen Square crackdown.

In Iran, the censorship has been more sophisticated, amounting to an extraordinary cyberduel. The government slows down Web access and uses the latest spying technology to pinpoint opponents. But at least in limited ways, users are still able to send Twitter messages, or tweets, and transmit video to one another and to a world of online spectators.

Because of the determination of those users, hundreds of amateur videos from Tehran and other cities have been uploaded to YouTube in recent days, providing television networks with hours of raw - but unverified - video from the protests.

The Internet has “certainly broken 30 years of state control over what is seen and is unseen, what is visible versus invisible,” said Navtej Dhillon, an analyst with the Brookings Institution, a research and policy institute in Washington.

But taking pictures is an increasingly dangerous act in Iran. The police in Tehran confronted citizens who were trying to film near a memorial to Ms. Agha-Soltan on June 22.

Threatening people who have cameras is only the latest in a series of steps by the authorities. On June 12, the day a disputed presidential election set off the protests, the government summarily shut down all text messaging in the country - the prime tool that government opponents had been using to keep in touch - making new tools like Twitter and old techniques like word of mouth more important for organizing.

The day after the election, Iran’s state-controlled telecommunications provider completely dropped off the Internet for more than an hour, according to Renesys, an Internet monitoring company. Access was partly restored two days later, a Monday. YouTube said traffic to the site from within Iran was down about 90 percent that week, indicating that most - but not all - connections had been stopped or slowed. Facebook said traffic from Iran was down by more than half since the election.

Despite the crackdown, the videos and tweets indicate that broadly distributed Internet tools cannot be completely repressed by an authoritarian government.

“You can’t take the entire Internet and try to lock it in a little box in your country, as China continuously attempts to do, said Richard Stiennon, founder of IT-Harvest, a Web security research firm. “There are just too many ways now to find paths around blockages. They would have to ban the Internet entirely, or build their own network.”


At rallies in Tehran against the disputed Iranian election results, cellphones and Twitter have thwarted government crackdowns.


State militia ransacked a Tehran University dormitory on June 15 as part of an effort to prevent the opposition from communicating.


Brian Stelter reported from New York, and Brad Stone from San Francisco. Reporting was contributed by Michael Slackman from Cairo, Steven Lee Myers from Baghdad, Noam Cohen from New York, and an employee of The New York Times from Tehran.