Please tell me the difference between a picture of a naked woman lying on a bed looking you in the eye in a sensual manner and a picture of a naked woman lying on a bed looking you in the eye in a sensual manner.
If the only purpose to the shot is to arouse you (as if a woman on the above pic was nicely displayed like an open oyster with some pink penis sticking out of her), then it is porn. If a image displays something more than nakedness and pinkiness (see above, enjoy beauty of her curves, displayed to the public in a manner that hides the most interesting parts, wonder about softness of her skin, which can be judged by light reflexes on her body etc.), then it's art. Erotic art. Easy.