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.

今年是中国1989年天安门民主运动的30周年纪念。当年，学生自发举行一系列游行示威，呼吁实施民主改革，中共领导人则选择使用武力镇压运动。中国红十字会称有2700名民众在武力镇压中身亡，但有不少研究机构指出死伤人数远不止这个。在2014年解密的一份美国政府机密文件显示，中国内部统计的死亡人数达10,454人。

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.

A new paper by the Citizen Lab investigates how Chinese censorship reaches independent developers and reveals that, while developers include censorship lists in open source projects, there is little apparent similarity in these blacklists, raising several questions about their origins.

本报告从技术层面分析微信如何过滤图片，并提出可能的反审查方法。

New Citizen Lab research reveals how China’s most popular app filters sensitive images and suggests techniques for evasion.

This report demonstrates the technical underpinnings of how WeChat image censorship operates and suggests possible evasion strategies.

加拿大多倫多大學公民實驗室（Citizen Lab）研究表明微信從一年多前就開始屏蔽與“十九大”有關的關鍵詞，隨著十九大日期逼近，該關鍵詞庫也在不斷更新。關鍵詞涵蓋內容非常廣泛，不僅包括了批評性言論，許多對中央政策和黨意識形態的中性指稱也被過濾。

加拿大多伦多大学公民实验室（Citizen Lab）研究表明微信从一年多前就开始屏蔽与“十九大”有关的关键词，随着十九大日期逼近，该关键词库也在不断更新。关键词涵盖内容非常广泛，不仅包括了批评性言论，许多对中央政策和党意识形态的中性指称也被过滤。