Why not say something like, "I know it's two years old, you've already mentioned it. I think it's great, though, because this way you get to see what she looked like when she was younger. I love seeing pictures of us when we were little compared to now. Plus that moment (since it's not a professional picture) looks like it was a great one, and he wants to share that great moment with you. I think that's awesome. Bean dip?" And if she STILL doesn't get a clue after that, I honestly would tell her, "Look, he didn't have to give you a picture at all, and the more you harp on it, the less inclined he will be to continue contact with you. Let it go, because I'm not going to hear it anymore."