"Pornography" is a subjective term. Pornography exists solely in the eye of the beholder.
"Art" is not subjective. It's an objective description of any creative work produced by artistic or handicraft techniques. Any formally posed photograph is "art", as is any painting, drawing, macramé wall hanging, or ceramic piece.
Any comparison of "art" and "pornography" is apples to oranges. It's not a valid comparison, since one term is subjective and the other objective. Any work of art may be judged pornographic by a narrow-minded or moralistic observer, but that does not make it so. Art is fact. Pornography is opinion. End of story.