There's many things you can do here in the states, but maybe you should be speaking to an attorney and/or to law enforcement in New Zealand. Good luck.
for Fairness & Your Freedom because sometimes good people find themselves in unpleasant situations
The response above is not intended as legal advice since it’s impracticable to provide thorough, accurate advice based upon the query without additional details. It is highly recommended that one should seek advice from a criminal defense attorney licensed in your jurisdiction by setting up a confidential meeting. Moreover, this response does not constitute the creation of an attorney-client relationship since this message is not a confidential communication because it was posted on a public website, thereby publicly disclosing the information, which is another reason to setup a confidential meeting with an attorney.
Your ex is a very stupid young man - making such a threat in a text message. Take it down to the local authorities and file a police report. Or, you could just give him back the watch, but even if you did that, you will never know for sure that he won't post the pictures anyway.
You might also want to contact the police where he is.
I certainly agree with my colleagues, but then again, perhaps consider looking into the best way to get the matter resolved without involving the police. When people start going down that road, it affects everyone. In some cases, you just can't avoid it, but it is potentially something that can follow you around for a long time. If the gift doesn't mean all that much to you, then return it, but be sure that he deletes the photo and has no other record of it. On another note, your ex is not the sharpest tool in the shed if he did put that in a text message. It is actionable.
The answer to this question is for informational purposes only and does not form an attorney-client relationship.