The judge.
https://en.wikipedia.org/wiki/I_know_it_when_I_see_it
The justice system is a computer made out of humans executing written programs called laws. As we've seen from decades of computer vision research, writing out an image classifier in a finite set of symbols is intractable. So instead the justice system queries an oracle (a human) to do the image classification.
Maybe in the future there will be a way to compile a learned image classifier into a set of directions in English and we will have laws that are followed by pages of what is essentially a small artificial neural network represented as an English flowchart, but I doubt it, that sounds dumber than asking a person to do it. You just have to make sure you're picking the right person to do the deciding.
We don't even have a tool that could reliably ID the subject of such a processed visual depiction.
Personally I think head-swap porns should be handled with defamation logic than general anti-porn laws. I find it more likely that I would be disgusted by deepfake porn of mine if I were to become such public figure that warrants it, than appreciating it, but it feels weirder that local police would be deciding whether am I to like it or not.
Although I might call out the opposite problem of making it a crime to request a sfw picture of a specific person and have the model generate something porny