Don't blame Shutterstock. As I recall the details, a judge hearing a dispute between Mike Tyson's tattoo artist and the producers of The Hangover 2 said the plaintiff had a strong case for copyright violation, leading the producers to settle. That led SS and other agencies to require a property release signed by the artist for any images with visible tattoos. They don't want to be sued, or to have it happen to their clients. Seems perfectly reasonable to me. A tattoo is original art, and the rights to that art belong to its creator, just as we own the art we create. So I either avoid models with tattoos, shoot them so their ink doesn't show or edit it out.