Chinese Google filter only works if you can spell
google.cn image search for Tiananmen: Gate of Heavenly Peace.
google.cn image search for Tianenmen, Tienanmen and Tiananman: Tanks, tanks, more tanks.
Try it yourself: Compare the same image search on google.com and google.cn. Only the results for “tiananmen” are different. Danny Sullivan at Search Engine Watch, who tracks these things for a living, has posted some screenshots.
Thanks to Allan Schaffer for helping me discover this by accident.