WeChat communications conducted entirely among non-China-registered accounts are subject to pervasive content surveillance that was previously thought to be exclusively reserved for China-registered accounts.
In this work, we study how Tencent implements image filtering on WeChat. We found that Tencent implements realtime, automatic censorship of chat images on WeChat based on what text is in an image and based on an image’s visual similarity to those on a blacklist. Tencent facilitates this realtime filtering by maintaining a hash index of MD5 hashes of sensitive image files.
In the days leading up to the 30th anniversary of June 4 1989, YY, a popular live streaming platform in mainland China, updated its keyword blacklists with content focused on Democracy Movement related memorials and activism in Hong Kong.
WeChat and Sina Weibo adapted and evolved their censorship efforts in response to the death of Liu Xiaobo.