If your tattoo is going to appear in a movie, you'll need a release signed by the tattoo "artist". In fact, you have to have a release signed every time you get a role---production companies each want their own. Make-up won't completely cover them and it takes hours and costs a lot for them to try covering them.
Justin Bieber is a lovely boy who appeared in a couple of episodes of a TV cop show and is actually a pretty good actor. But now he's plastered with tattoos and that career's been closed off to him. Of course, not many young men want to be "lovely boys" and that might explain why Bieber decided to horribly disfigured himself.
And being tattoo-free would be a boon to a career in pornography.
Obnoxious Hollywood moron Shia LaBeouf is now walking about with some crude-looking tattoos on his thighs. Marlon Brando would show up on movie sets without pants---he was terribly overweight and only wanted to be filmed from the waist up. Maybe LaBeouf doesn't want his thighs being shown on screen.