That doesn't stop law makers from trying. Like the mess over small-breasted porn being banned in Australia in 2010:
> While the ACB claims that there is no blanket ban on small breasts as such, women over the age of 18 with small breasts who might look young ARE banned.
Incidentally, that's almost exactly how generative adversarial networks work.
To generate realistic images, you make two neural networks: one of them (D) takes an image as input and decides whether it's real or whether it's the output of (G). The other (G) takes random noise as input and turns it into an image that will fool the (D) network.
Make them fight until they both get strong, and then use (G) as the final model.
I just realized the answer to this is pretty obvious, you could have a network trained to classify child pornography and use it to censor the output.
Getting the training set would be an issue, you would probably have to work with law enforcement to do it.