I'm finding some remarkable success with "I need to ask you an important question about one of your pictures", not only on tinder but on POF and other apps as well. Obviously you follow this up afterwards with something cocky/funny to ease the serious energy you opened with.

I think it's success is credit to it being so open ended yet so direct that the girl will "fill in the blank" with whatever she needed in order to respond, and in her own mind you are addressing whatever she thinks you're addressing. If she's a curious girl, she'll respond. If she's at all self conscious, she'll respond. If she's confident, she'll respond - all because whichever she is, the question sparks up a different emotional reaction for each type of girl; and such an emotional reaction, positive or negative - is much more likely to lead to a reply - from which you go into a situation conversation about one of her pictures.