[Age of Ignorance]

I would be very hesitant about making "revenge" plans. That's not appropriate in any relationship; anything done out of spite creates more problems and will eventually blow up.

I'm actually afraid this conversation would have no issue if the OP was a male and his girlfriend was keeping naked pictures of old boyfriends to show off to her girlfriends. The point is, what he has done is wrong. But unfortunately, some men don't take active steps to delete these sorts of things, even if they never use them for any purpose whatsoever. His excuse that he shows it off to his mates may be a lie, but it could also be the truth. Regardless, that isn't your problem - it's the ex-girlfriends'. It certainly doesn't mean he is doing anything with them, but it doesn't mean he isn't.

I'm afraid otherwise you're in a bit of a pickle. Talking with him may get nowhere, but you do need to air your grievances about this so that he knows where you stand. Let him justify it however he wants, but ultimately, this isn't a solveable problem even if he does delete the pictures. It may strain the relationship, and you just need to remember - or convince yourself - that it's in the past and it doesn't effect your relationship... or at least, it shouldn't.