What are the copyright laws concerning explicit pictures given to someone by their significant other?

I think this is a moral issue as well as a legal issue. She's your ex now, but she gave you these photos when she was your current girlfrend, and she trusted you. Even if she never expressly said, "don't ever send these to an amateur porn website or share them with your buddies," unless you specifically know that those kinds of uses were fine with her and that these photos were not meant to be private, you have to assume those uses are NOT fine with her and they were meant to stay private between you and her.

As for the legal side of this, in California, making these photos public by either of those uses you mentioned would likely give her claims for invasion of privacy and intentional infliction of emotional distress. Both are torts and would expose you to compensatory and punitive damages.

My advice is to send her back the photos.

Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.

Distributing nude photographs of a former girlfriend is not, unfortunately, "illegal" in the sense that it violates criminal law (though there are exceptions).

As Ms. Koslyn notes, however, the former girlfriend could very well sue under state privacy laws. Make no mistake: if a person knows that what he or she is doing is wrong, a judge or jury will either fit or find a rationale to punish the person for doing it.

In this case, distributing nude photographs of a former girlfriend without her permission is so repugnant to morality that she will likely have little trouble finding a good-hearted -- and ticked off -- attorney who will handle her case pro bono, make the fella's life (and his friends' lives) miserable, and keep him tied up in litigation so long that his bank account can longer sustain the petty vindictiveness that motivated him to distribute the photographs in the first place.

So ... legally it's wrong, morally it's wrong, and economically it's wrong.