Interesting post. Certainly the paintings aren't pornographic (although like the Supreme Court I can't define pornography but know it when I see it). The depiction of the female nude has a long history in art, and so, for that matter, does the male nude. Does anyone consider Michelangelo's David porn? The very question is absurd.
I have heard of some who wanted to cover reproductions of David. There were also some cardinals who ordered the loin cloths to be added to Michelangelo's Last Judgment in the Sistine Chapel.
To me, nudity alone is not pornographic, and many on this thread nailed that. It has to excite to be pornographic. (But, of course, different people are excited by different things....let's not go there.)