OK, I'll skip the moral advice and go right to the practical:
If you work with her, showing the picture around the office and/or using it to raz her could be considered sexual harrassment. You could end up in a heap of trouble buster.
OK, so let's suppose that your moral compas is out of order and you don't care about getting your butt sued...
Do you want to be friends with her after this is all over? If so, I would suggest talking to her and finding out what she thinks.
Consider the following: Is it the kind of professional photo that might have been published somewhere or is it a raw naked photo that might have been put on the internet by an angry ex-husband?
If it's the former, maybe she already knows it's out there and is OK with it. If it's the latter, you don't want to be viewed as no better than that rat-bastard who put it on the net in the first place.
Either way, talk to her and find out how she feels.
So, let's review:
If your moral compass is out the window *and* your employment isn't an issue *and* you don't care if you remain friends, you *still* might want to keep it to yourself for one basic reason: You can admire her naked body without having to share the pleasure with anyone *and* without her knowing about it.
It's kind of a voyeur thing.
So, maybe doing the right thing is more fun after all?
