I'm not a lawyer but I'd recommend against using real people's likeness in your renders. Here are some considerations.
1. The law is against you. You are not allowed to use another person's likeness, especially for porn when you can't honestly claim you're just parodying them.
2. No one is likely to ever found out that you did use someone's image. The internet is huge and people have other problems on their head than looking for random people doing their porn images.
3. Even if a celeb did find out you have rendered their image fucking dogs, the reasonable response would be to ignore it and let it drown in the overall internet noise, for fear of invoking the
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, i.e. if they do come after you, everyone will see the images of which they'll otherwise be oblivious to.
4. Finally is the human factor: people are unpredictable. It might be unlikely for the celeb to find out you have used her image and not very wise to come after you, but you might get unlucky and really piss someone off, a person who will come after you regardless of the damage it may do to them. Do you with to take that risk? Your call.
So: the wisest way to use celeb figures is for your personal "amusement" only. The second wisest is to share them anonymously, without associating them with anything related to profit (thus tying them to you). Finally, you can take a risk and try to make money and hope everything will be all right. It might turn out fine and it might turn out very very bad.
Good luck!