I think some of those images would be more at home under goth, which is more clearly defined with fashion that includes "dyed black hair, black lips and black clothes". Both goth and emo stem from musical genres and their resulting cultures, but from what I understand (mostly from this post ), if they're wearing all black with black lipstick and black nailpaint, they're likely goth. If their outfit is mostly black with some colorful accessories, they're likely emo. As I understand it, this is goth and this is emo, for example.
I have no justification for why emo is being tagged on completely naked and otherwise unmarked characters.
Updated by anonymous