I'm not sure that artistic nudes can't also sometimes be pornographic- I have seen some images in my time that are both beautifully artistic and definitely highly sexual and sexually moving. For me personally, my distinction lies in the quality of the image- is it reasonably original? Well drafted? Is the lighting carefully created, is it an image that you keep looking at after you've brought yourself to orgasm?
It's highly subjective.
On a personal note, I do fine art nudes (I'm waiting on quite a few to add to my port, shot on film so it takes time) and my selection process includes that what we are trying to do is make art- We might not succeed, it may not turn out well and the intention could vary greatly, but I don't shoot stuff that's just intended to titillate without artistic merit and ability and talent do make a big difference in the final product- and when original, talented and skilled individuals make porn- well I think it's a new genre- Art Porn.
in figure drawing the rule of thumb was the lack of clothing plus anything else would emphasize sexuality. so a nude woman wearing a necklace and socks or a nude man wearing eyeglasses, etc. i would reference euan uglow to disagreed with this point as his figures often are nude plus say a small shirt or article of clothing and i would think it very hard to argue against his working running the classy, sophisticated and very valuable art side of nudes. i also dont think this applies to photography the same as it does painting but i find the general rule to be interesting if nothing else.
The more explicit the image, the more likely it will be interpreted as smut. But, no degree of nude content automatically eliminates an image from being art. Conversely, artistic intent does not guarantee artistic output.
For me, it's an image where the model is nude, or effectively nude, and the goals are "artistic." Which is most of my work, because other styles tend to bore me. Some of my stuff has a bit of fashion to it, but still.
To the OP; I think of images as "art" if that's the way it was approached, and that was the goal. Certainly, some people are better at it than others, but at least in my mind, I can usually tell what was intended as art.
Santa Barbara, California, US
I will not even try to speak for everyone but for me personally if I look at a nude image and it hold my attention, makes my eye travel around the composition, makes me think and interpret the energy... And then if I go back days later and I sometimes see a different interpretation in the same image, I will then call it art.
Technical aspects of the image can be a combination of millions of things but the final print determines in my mind if it is art.
Maybe not for others but for me is all that counts.
Someone once said that a work of art and a work of pornography both instill desire on the part of the viewer.
The difference is that with pornography the viewer desires the subject depicted in the work, whereas if it is art, the viewer desires to possess the work of art--the painting or print--itself.