You can’t say “I’m going to besmirch your good name (release the pictures I have, etc) unless you pay me $”. That’s blackmail.
You can say “”I’m going to besmirch your good name (release the pictures I have, etc)”.....then the person offers to pay you money to go away.
Blackmail is putting the other person to what is legally an impermissible choice. You just have to leave off the “unless you pay me” part and let them fill that in themselves. Then its not considered blackmail.
per FLT-bird
Yep. Its legal to have it. Its legal to sell it. You can even sell it to them BUT you cannot put them to the choice of Your money or.....(negative consequences for them).
However if you don’t offer the choice....if they offer to buy it from you without you having offered to sell it to them, then its legal.