A picture hanging in an office space (including a cubicle) is potentially visible to co-workers, if not clients or customers. If the picture offends someone who has to walk past it regularly, for any reason, and if that person finds it offensive, then it could become a harassment issue. According to the U.S. Equal Employment Opportunity Commission's website:
It is unlawful to harass a person because of that person's sex. Harassment can include "sexual harassment" or unwelcome sexual advances, requests for sexual favors, and other verbal or physical harassment of a sexual nature. Harassment does not have to be of a sexual nature, however, and can include offensive remarks about a person's sex. For example, it is illegal to harass a woman by making offensive comments about women in general. Both the victim and the harasser can be either a woman or a man, and the victim and harasser can be the same sex.
The Commission explains that general teasing, offhand comments and isolated incidents are not considered harassment; the law is meant to protect against ongoing, offensive activities that create a hostile or uncomfortable work environment.
How am I supposed to know if I'm offending somebody? Uh, duh? Legally, a person who is bothered is required to tell the offender or work through the company's formal complaint system. And anyone in their path is required to respond and accommodate the person who is being made to feel uncomfortable. But it does not take a rocket scientist or an HR Manager to recognize offensive behavior. Pay attention to the people around you. When they say, "That picture creeps me out," or "I wish you wouldn't call me that nickname anymore," they are, without hitting you over the head, telling you they are bothered.
The same rules apply to all kinds of harassment: race, sex, religion, national origin, age, disability, or genetic information.
So does that vintage advertisement constitute harassment? Only if it bothers someone, and only if they say so. But use common sense: if you post, state, remark, or even think of something and wonder if that was okay, chances are, it wasn't.