While still subjective, to say the least, pornography is defined as;
Merriam-Webster said:
1: the depiction of erotic behavior (as in pictures or writing) intended to cause sexual excitement
2: material (as books or a photograph) that depicts erotic behavior and is intended to cause sexual excitement
3: the depiction of acts in a sensational manner so as to arouse a quick intense emotional reaction <the pornography of violence>
Anyone can say that even these definitions are subjective where "eye of the beholder" is concerned. Somewhere there is an artist who took a photograph of a beautiful man or woman nude and called it art only to have someone else look upon that same photograph and became sexually aroused! The very same thing can be said for photographs of fully clothed men and women! There would almost certainly have to be a general consensus that what is viewed does/doesn't elicit such a response then it can be called art/pornography. The next question is who can be nonobjective in making the final determination? I suppose, in this case anyway, a judge or jury.
A sticky wicket, for sure.