This is an interesting case of copyright law. the tattoo artist Victor Whitmill holds a copyright registration for the tattoo. and the reproduction shouldn't fall under fair use because the movie is obviously not paradoying the tattoo or mike Tyson it is simply a specific reference to Mike Tyson's distinctive face. Essentially the tattoo artist is claiming that mike Tyson's face is no more then a billboard used to display the artist work.
This creates a problem for people with tattoos. Because it is stating that a tattoo artist should receive royalties when the person with the tattoo shows the tattoo in any form of entertainment or advertising.
I disagree with the tattoo artist in this case. There is no doubt that the artist holds the copyright to the tribal design. and there is no way Warner brothers can advertise that design by itself or use it as any sort of logo for the movie. But the tattoo artist does not hold any copyright for the tattoo on Mike Tyson's face. Because even if Tyson signs a contract stating that the artist still retains ownership of that design that artist will not be able to own copyright over Tyson's face. The object being sued over,the fake tattoo on Ed Helms' face, is a specific reference to Mike Tyson's face. Had the production gone a different direction and placed the tattoo on Ed Helms lower back like a tramp stamp then the artist would need to be paid royalties. But this wouldn't happen because no one would actually recognize that design were it placed above Ed Helms' ass.
What it comes down to is this. when you receive a tattoo that tattoo belongs to you. That ink is in your skin and the pain in getting it is your pain. And you are the one who walks around every day wearing it not the tattoo artist. So if some idiot takes a marker and draws a copy of your tattoo on themselves they are imitating you not the tattoo artist's designs.
If Warner brothers loses the cases or more likely pays out a settlement they could make their money back and then some by the precedent it would set. All they have to do is put their copyright trolls on the task of going after every tattoo artist who has tattooed any copyrighted materiel that Warner brothers owns for example; Looney tunes and DC comics. Judging from the tattoos displayed on his website Warner brothers could even just make their money back from Victor Whitmill himself by Joining the Frazetta estate in a case against him.