"Basically, there needs to be something in the picture that makes it clear that the girls are more than just friends, otherwise it is not yuri."
Do female friends lay across each other naked and spread apart their friend's pussy? Oh god where have I been all this time?
Seriously though can someone who actually knows what they're talking about tell me if this qualifies as yuri or not. The general opinion seems to be rather skewered these days and I'd rather not start a forum topic.
She's touching the other girl's vagina, I'm sure if there were an image of a guy touching another guy's penis in a similar position it would be tagged yaoi.
She's not presenting herself, the other girl is the one spreading her apart. It isn't exactly something two friends do since she's an inch away from fingering the other girl.
*late to the party* Doesn't seem yuri to me, since neither girl is seeming to involve themselves as the partner of the other. Rather, one girl is facilitating a partnership of the other with an unknown third.