While this conduct may offend you, it may not be considered against the law; courts have generally declined to establish a "code of conduct" or make all conduct of a sexual nature in the workplace illegal. The answer might be different if your coworker posted photos from the magazine in a common area where everyone could see or that could not be avoided in the course of your work day, since that would more directly affect your work environment by forcing you to view sexually graphic material against your will. If you have told your coworker that you find it offensive, and the situation continues, you may wish to discuss it with a coworker, supervisor, or human resources manager to determine whether others are offended, or whether your company has a policy that would be violated by this behavior. Perhaps a solution can be reached that does not involve filing a formal complaint or lawsuit.