I think many of Edward Weston's nudes are transparently sexual, but not pornographic. It's even harder to see them in a purely aesthetic light when you know he was a sexual fiend who shared his girlfriends with his sons. To me, Weston's beach nudes represent the writhing obscenity of nature - the idea that nature is simply a slut, putting itself on display. With somebody like Wynn Bullock, there are no ecstatic symbols of sex in his nudes, and there's plenty of context in which, you could say, sex becomes only a part of nature, rather than the whole. I tend to think in most cases an attractive nude alone, against a black background, has the biggest effect when it arouses - all that is aesthetically pleasing about the image then pales in significance. The more conventionally attractive the model, perhaps the more context is needed to balance the 'arouse-effect' scale. The biggest factor then might be the qualities the photographer looks for in a model. From most of the amateur nude work I've seen, I'd say he simply picks his ideal mate nine times out of ten. For his own purposes in that case, he is a pornographer. But... unless all his models look like Kim Kardashian (where his intent becomes obvious) people are unlikely to label it porn. With the nude, it pays to have strange taste in women, if you have no objectivity as an artist.