Here's a preview of those leaked pics we talked about last week.

Apparently, the pictures are going around now because of a girl Demi is kissing in one of the photos.  Supposedly, Demi is BISEXUAL, and the two of them had an on-and-off fling for a while.

She broke things off after Demi got back together with WILMER VALDERRAMA, then she gave these pics to a male friend and he's the one trying to sell them.  In addition to nudity, the guy says some of the pics are of a SEXUAL nature.

I can't post them here, but CLICK HERE if you'd like a peek.

Brian Lindensmith / Splash News / (C)