Jigokudani-yaenkoen is a Japanese natural park that's home to a number of wild snow monkeys. It's fun to watch them hanging around and soaking in the area's hot springs.
The park's English-language website offers this helpful advice on telling the monkeys apart:
It's very difficult to distinguish monkey's face, like we can't memorize foreigner's face. But, if you keep up to observe them, it's become easier and easier to distinguish their face.In that last sentence, I think they're talking about monkeys, not foreigners, but I'm not sure.