It is not only harassment, it verges on blackmail. If your Ex is seeking some quid pro quo from you it is blackmail and you should call the police.
Be aware the police will only wish to become involved if he is seeking something in return for not posting the pix. Otherwise, they will tell you it is a civil matter.
As to the civil matter, a harassment suit will cost you over $20K in legal fees, and you will be hit with counter claims costing you another $20K in legal fees.
My best counsel is to ignore the bully, lie low and let this all blow over.
This post is provided for general informational purposes only and is not intended to be legal advice specific to you. This general information is not a substitute for the advice of an attorney in your jurisdiction. The attorney client relationship is not established by this post.
Much has been posted about this subject. http://www.avvo.com/legal-answers/someone-hacked-my-boyfriend-s-account-and-now-nude-1276343.html#answer_2532751
Contiguglia / Fazzone, P.C. / Standing up for you, when others sit down! / www.contifazz.com / Just because I answered your question, that does not create an attorney - client relationship between us unless and until there is a written fee agreement in place formalizing our attorney - client relationship.
There are a number of possible legal theories, depending on the law of your jurisdiction: if you took the pictures, you would be copyright holder, there are privacy rules. None of these might matter if you gave permission to use them (which you kind of did by sending them to him).
Depending on the source of law, outcomes may vary. The only for sure thing I can tell you comes from this steadfast rule of life: nude photos you text will end up on the internet.
This answer does not create an attorney-client relationship. Please contact a lawyer qualified in your jurisdiction to discuss your situation in confidence. The guidance I have given describes only general legal concepts without knowing the exact factual details of your situation.
I agree with my colleagues, there are a number of different possible legal theories. Not only would you have a criminal cause of action against him, but also a civil case against him as well. I suggest you contact an attorney in your area immediately.