[null, {"document_url": "http://mediacitizen.blogspot.com/2013/11/the-faces-of-social-media-censorship.html", "unformatted_src": "http://3.bp.blogspot.com/-1QhQXVCP51U/UoY-qQs3ivI/AAAAAAAAKEM/tsdpLHr9lnw/s400/Weibo1.jpg", "src": "http://3.bp.blogspot.com/-1QhQXVCP51U/UoY-qQs3ivI/AAAAAAAAKEM/tsdpLHr9lnw/s400/Weibo1.jpg", "formatted_filename": "Weibo", "rendered_width": 300, "rendered_height": 400}, null, {"document_url": "http://mediacitizen.blogspot.com/2013/11/the-faces-of-social-media-censorship.html", "unformatted_src": "http://2.bp.blogspot.com/-cmELyzhZ5e0/UoZHJ8XpC7I/AAAAAAAAKEc/se__2za-EFc/s400/weib4.jpg", "src": "http://2.bp.blogspot.com/-cmELyzhZ5e0/UoZHJ8XpC7I/AAAAAAAAKEc/se__2za-EFc/s400/weib4.jpg", "formatted_filename": "weib", "rendered_width": 277, "rendered_height": 400}, null, {"document_url": "http://mediacitizen.blogspot.com/2013/11/the-faces-of-social-media-censorship.html", "unformatted_src": "http://4.bp.blogspot.com/-KOLyusttBHs/UoY-o6WqWkI/AAAAAAAAKEI/Eq8w3NSlX-8/s400/Weibo3.jpg", "src": "http://4.bp.blogspot.com/-KOLyusttBHs/UoY-o6WqWkI/AAAAAAAAKEI/Eq8w3NSlX-8/s400/Weibo3.jpg", "formatted_filename": "Weibo", "rendered_width": 300, "rendered_height": 400}, null, null, {"document_url": "http://mediacitizen.blogspot.com/2013/11/the-faces-of-social-media-censorship.html", "unformatted_src": "//lh3.googleusercontent.com/-1_CZwqunjEQ/AAAAAAAAAAI/AAAAAAAAHog/1LvfhLXTCB4/s80-c/photo.jpg", "src": "http://lh3.googleusercontent.com/-1_CZwqunjEQ/AAAAAAAAAAI/AAAAAAAAHog/1LvfhLXTCB4/s80-c/photo.jpg", "formatted_filename": "photo", "alt_text": "My photo", "rendered_width": 80, "rendered_height": 80}, null, null, null, null, null]

Self-Censorship from Beijing to the Bay Area Online news organization ProPublica on Friday launched a special feature documenting censorship on social media in China.

China's Memory Hole focuses on censorship of users of Sina Weibo, the Chinese equivalent of Twitter, which filters out "undesirable" content from the more than 100 million items that are posted there daily.

A team of ProPublica writers, technicians and translators combed through deleted items after gaining access to and monitoring Sina Weibo's network over a five-month period.

ProPublica is vague -- perhaps intentionally -- about the actual mechanics of their monitoring.

We do know that China has assigned the task of blocking social media content to the privately held companies that run the services. It’s a comprehensive self-censorship approach that keeps the companies guessing on the limits of appropriate public discourse.

Sina Weibo censors walk a fine line in China, ProPublica Reports. "If they allow users too much freedom, the government will shut them down. But if they block too much material, the users in this quasi-capitalist economy can go to one of the company's competitors."

U.S.-based social media also grapple with self-censorship. While circumstances differ from those at Weibo, the results are often as arbitrary and confounding. In August, Facebook removed artist Erik Ravelo's image of a priest and child (right), which, according to Ravelo, was created to address child abuse within the Catholic Church. Within days Facebook also took down Ravelo's fan page.

In April, Jeffrey Rosen of the New Republic noted that Facebook's censorship program is run by a young corps of earnest and well-intentioned "deciders," who frequently make the wrong calls.

Those on the receiving end of a Facebook block are often left without a clear explanation for the action. Many users of Facebook, Twitter and YouTube may see these and other social media as soap boxes for free speech. They're not.

ProPublica's Weibo initiative gives us a rare and devastating glimpse at the faces of Chinese censorship. In one (top), a woman protests the death sentence the government's handed her father, and appeals for clemency.

In another (right), a family stands outside their home holding signs that read "Protect My Homeland." They've arranged four propane canisters in front of them to signal that they mean to fight the city planning office's order to demolish the building.

Weibo has deployed hundreds of human censors to do what machine filters can't: identify subtleties in language and imagery that Chinese often use to get around the nation's firewalls.

To many, Chinese censorship feels like a last-ditch defense against the invasion of newfound Internet freedoms. But the government has managed to mobilize the private sector to effectively beat back the advance.

Meanwhile, U.S. social media are still searching for a more perfect screening system. According to Rosen, Internet companies are exploring the use of algorithm that could predict whether a given user's post crosses the line that separate appropriate from "inappropriate" content.

"Hoping that the machines will one day police themselves amounts to wishful thinking," he writes. "It may be that U.S. constitutional standards, applied by fickle humans, are the best way of preserving an open Internet."