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.
You are talking like you are really desperately trying to convince yourself that it isn't porn. Why would someone take a photo of him/herself naked without it being for erotic reasons? (except if it's for medical reasons) Erotic art = porn.