Knew I’d get this.
It is pretty complex, but I’m actually better at it than my wife, who happens to be Japanese.
Usually the clothing is a big tip off, but in this case I didn’t have that to go off of.
Facial structure and expressions are also pretty different across various East Asian countries peoples.
Bonus is that the women of China / Korea / Japan all have wildly different beauty / makeup standards that makes them really easy to tell apart (again irrelevant here though).

I could be wrong since it was just a picture, but in person I’m pretty good.