I'm pretty tired of people quoting whomever said that he can't define porn, but knows it when he sees it. The quote has two essential implications.
First, that the classification of pornography is intuitive rather than explicitly rule-based. I agree with this.
Second, that there is no fuzzy border between porn and non-porn. This I take great issue with. If you take all of rated-R movies, nude photography, sculpture, and the websites calling themselves the "pig-butt nastiest site on the internet", you see a great variety of stuff, much of which is very hard to classify as porn or non-porn.
And the thing is, most of what people say is like porn in the way quoted is also that way. That is to say, when someone says "like porn, I know x when I see it," he or she is probably wrong about x. Fuzzy boundaries are everywhere.
pictured is porn. Or is it?