If you took the photo of the rock star, you own the copyright in the photograph, but the rock star owns the rights to his image.
Famous people often capitalize off their fame by selling their name and their image to companies that will pay them BIG bucks for endorsements. In fact, many famous people make more money from their endorsement deals than they do in the field that made them famous - the Brad Pitts and Jennifer Anistons and Tiger Woods of the world (well, maybe not so much Tiger Woods any more) make much more selling their name and image for use by a company than they do with their films or their sport.
If you wish to use the photograph you took in a commercial manner, you must seek out the rock star and obtain his/her written permission to use the photograph. . . . or risk a lawsuit.