Nudity does not automatically equal pornography.
If we’re going to talk about pornography in a Catholic context, perhaps it would be useful to be reminded of the CCC definition of pornography:
2354 Pornography consists in removing real or simulated sexual acts from the intimacy of the partners, in order to display them deliberately to third parties. It offends against chastity because it perverts the conjugal act, the intimate giving of spouses to each other. It does grave injury to the dignity of its participants (actors, vendors, the public), since each one becomes an object of base pleasure and illicit profit for others. It immerses all who are involved in the illusion of a fantasy world. It is a grave offense. Civil authorities should prevent the production and distribution of pornographic materials.
By the above definition, not even the display of an erect male organ would be considered “pornography”. Certainly viewing an erect male organ would not be “pornography” for me, and wouldn’t even be considered leading me to lust, but a homosexual man or a woman viewing the same image might have a different reaction.
A large part of pornography is in the eye of the beholder; for me, the above definition of “pornography” hardly is pornography in my eyes simply because it thoroughly turns me off, but it is pornography in its intent and thus sinful.
We are therefore responsible ourselves for avoiding erotic images that cause us to lust. For some it can be a lingerie billboard, and for others, nude art.
Taste, good, mediocre or poor, is another matter altogether. I have seen a lot of religious “art” that is in very poor taste but not even remotely involving nudity.
I guess I see roughly three levels: nudity (non-erotic), erotica, and pornography. But the lines are blurred by individual sensitivities and what turns us on.