I don't get it. Why not just post non-nude promo with the bra/panties/clothes/whatever still on? Then say "paying members get to see me nude" or something like that? At least then you can still see her body and her curves, cleavage, etc. A hot babe still looks sexy in nice lingerie, bikini, tight clothes, etc. Some people like the tease of nice tits in a sexy bra or awesome ass in sexy panties.
Another one I don't get in image sets is when girls take off their bras but then cover their tits with their arms. Why not just leave the bra on? At least then we get to see the size and shape of the tits. Some tits actually look better in a good sexy bra or bikini top.
.