Thatís why it continues to be such a furious debate, because the line between them is often very fine and indistinct.
Offhand Iíd be tempted to say that art tends to be more tasteful than porn, but thatís not really the definition, as Iíve seen very good examples of tasteful and artistic porn.
I have to say the whole thing annoys the hell out of me; we have to fight this conservative racket to knock any nudity out of art. I even got flack for it once at school, for IMPLIED nudity (the picture frame cut off about the shoulders on a female subject and did not even show breast, much less nipple, the fact that it was brought up at all proves my instructor was an idiot.
I tend to think if the work of art, photography, etc. is made for the clear and obvious purpose of arousal, then itís likely porn, but even that isnít a perfect definition.