My son is way too young for this, so feel free to tell me i'm wide of the mark but I'd:
-forward the photos to your phone, so you still have them as evidence
-Sit her down and tell her that you've seen the photos
-Say that you understand that X is a family friend, and that is a mutual activity between the two of them (so not coersion) but what steps has she taken to stop him publishing these online if they split up / he decides he doesn't like you? It might danw on her what she's done.
For now, I would give her a phone with no internet or camera, so she can still contact you when she's at her dad's. I would also be having a conversation with the boy's parents about this, possibly before the one with your daughter, so she can't warn the boy before his parents find out and give him time to delete photos.
I'd be more concerned, I think, if this was your DD and someone over the internet unknown to you, or coersive in some way, but however she wants to express herself to him, however pornographic the language, she needs to understand that she can't control photos or text once she's sent them to someone else; in this case, I'd be more concerned about him having such photos of her than about the language she's using, presuming his language is as explicit as hers.