‘Nudify’ Apps That Use AI to ‘Undress’ Women in Photos Are Soaring in Popularity::It’s part of a worrying trend of non-consensual “deepfake” pornography being developed and distributed because of advances in artificial intelligence.
I don't think any of the models they're using are trained from scratch. It would be much cheaper to take something like Stable Diffusion and finetune it or use one of the hundreds of premade porn finetunes that already exist.