Tell her you wanna show her some pictures, and go through a couple of pictures of you and her, some pictures of places you've been, and then lastly that picture you found on the cell. I feel for you, I'd probably react the same way as you, at least you've only been seeing her a couple of weeks. Don't post her pics on the net, seeing those pics hurt but didn't kill you. After her explaination (wait for her to explain) get her to go as far as she can and then dump her. Worst things could have happened. (It'd be especially painful if you didn't get oral from her or sex and she did this to that guy faster without being his girl)