I've been living here in China for 7 years now, it's easy for me to tell different Minorities / Regions (ie Sichuan, Jiangsu, Shanghai) just by the face.
Though, once we start going to Northern East China, the Manchurian side, it starts getting difficult.
Koreans by the large, have smaller eye lids compared to most Chinese (more close together) they also tend to favour having operations to make them more wide eyed. In fact, most Korean TV/Film stars have undertaken some form of Cosmetic Surgery to the face.
Also, since being a Minority from NE China, they tend to be taller/larger than their western cousins. The further South of China you go, the smaller they seem to be.
(that should be the end of the post, as I'm quite good at doing that)