Every day, more than 100 million items are posted to Sina Weibo, the microblogging service sometimes called "China's Twitter". And every day, teams of censors comb through the posts in search of anything that changes what the government likes to call a "harmonious society."
For the past five months, ProPublica has been quietly watching the watchers by using software to monitor 100 Weibo accounts. Every post containing an image is monitored to see if it is deleted. Of nearly 80,000 posts, about 5 percent, or 4,200 posts, were deleted by censors.
ProPublica launched an interactive feature that allows readers to see and understand the images that censors consider too sensitive for Chinese eyes. More information on how they did the story can be found here: http://www.propublica.org/article/how-we-observed-censorship-on-sina-weibo.