Pantyfanatic,

I don't know about Mona Lisa's panties; when I was there I didn't see much because I'm not tall enough to see over all the other tourists. But I could see that the frame went around the edges and added to the picture. It didn't just cover everything up!

From the expression on her face I suspect she's not wearing any (well prove I'm wrong!). And she certainly would not spoil her nice rolling butt with a visible panty line.