Not unique as in 'different'
Unique as in 'marked'.
Ie the exact same picture, but sized differently, or encoded at a slightly different rate. Or maybe with a small dot photoshop'ed in.
Very easy to do. You'll never know which one.
Besides - it's not likely the five will ever even know each other. Five people randomly paid $500 or something dollars for that one topless set. How could they possibly even know each other?
Never going to happen. Never going to be released. No chance - give it up.