What should I do if my girlfriend has a picture of me naked and I want to dump her?

Suck it up and take the consequences.
You reap what you sow, so either get it back BEFORE you dump her, or be prepared for the backlash.

Digital picture? Ah it doesn't matter, just go and talk to her as a mature person and explain to her that you'd like the picture back. If she gives it to you or not, dump her anyway because there's nothing that you can do about it aside from sneaking into her room one night like a ninja, go through her belongings, find the picture and dispose of it.

Wait, do you want to dump her BECAUSE she has a picture of you naked or because you want to dump her and not have the possibility of your picture being posted all over the internet? Why can I relate to a lot of these situations? I have about 5... um... videos of my ex (again with the ex) doing some very grown up activities. I feel that she did me dirty and we're now going through a breakup (a very peaceful breakup, it's weird), but I would NEVER, EVER post those videos of her online (trust me, I could do it very easily). It speaks of a person's character to stoop that low.

Erase the picture? Maybe a little virus on a computer from one of your tech savvy friends? Just kidding...

Ask her to give it to you, if she doesn't... Oh well... is not like she can use it against you.

Why are you dumping her, and what kind of person is she?