What government could bring itself to block an image like this?

To censor the Internet painlessly, undetectably, is the dream that keeps repressive governments up late at their mainframe computers. After all, no users are so censored online as those who never see it.

The Iranian government is carrying out an Internet crackdown in hopes of subduing the protest movement that has surged since the disputed results of the presidential election on June 12. At the same time, the Iranian government has been sending out the police to restrain protesters and foreign journalists.

Thus far, however, the Iranian government has learned the difficulty of trying to control the Internet in halfsteps. Because the government’s censorship efforts are so evident - transparent, even - there is a battle raging online to keep Iran connected to the world digitally, and thus connected to the world. Sympathizers abroad are guiding Iranians to safe access to the Internet and are hosting and publicizing material that is being banned within Iran.

If only Iran’s leaders had thought through the implications of what can be called the Cute Cat Theory of Internet Censorship, as propounded by Ethan Zuckerman, a senior researcher at the Berkman Center for Internet and Society at Harvard Law School. His idea is simple: most people use the Internet to enjoy their lives, and among the ways people spread joy is to share pictures of cute cats.

So when a government censors the Internet, it had better think twice: “Cute cats are collateral damage when governments block sites,” Mr. Zuckerman wrote for a recent talk. People who could not “care less about presidential shenanigans are made aware that their government fears online speech so much that they’re willing to censor the millions of banal videos” and thereby “block a few political ones.”

As it happens, Mr. Zuckerman said, the Iranian government’s censorship task has been made harder because there is a thriving blogging community there, which he attributes to an earlier Iranian censorship campaign against traditional print media, in 2003. Writers flocked to the Internet. This fact, combined with a history of blocking access to social media tools since at least 2004, means that a group of computer-savvy communicators “have had five years to figure out” how to get their message out.

They have learned about all manner of “proxies,” that is, improvised ways of evading censorship - often connecting to a computer outside of Iran, which then can connect to the Internet freely. In earlier cases, the important news that bloggers had to share on a social network might have related to soccer, or a certain favorite pet, but today those same tools are used to get the word out about protests and a spirit of defiance within Iran.

There are practical benefits to the mainstreaming of political protest online. It presents another barrier to censorship. Beyond the practical benefits, there is also something satisfying about a country being assisted by ordinary bloggers who suddenly show their skills in organizing and belief in basic political principles.

But, Mr. Zuckerman reminded me, “You have to have the sword at home. You don’t want to have to buy a sword at the last minute.”