I see. So not only are they in posession of child pornography, but they also intend to distribute it. That is literally illegal and pretty damn bad. I would suggest you tell that to them and phrase it that way so they think about what they're ACTUALLY doing, aside from revenge or anything. If these photos weren't already posted publically, then that person is also performing unauthorised distribution and defamation. I don't know if the police would be bothered or not, but the official "legal" route is definitely something I'd look down before doing something silly like bribing them or giving into blackmail. Do keep in mind you've produced child pornography (of yourself). I am not a lawyer and this isn't legal advice.