But personally I think a poster is a large image piece on a medium with words and if there is no image then the type is designed as an image. The poster is not fine art but a graphic design that is concerned with communication using words and image.
Like an illustration or an advertisement and unlike a painting, a poster must be superficial—what is to be communicated should be on the surface, easily understood. On the other hand a poster is not like an advertisement which has a very specific purpose and a specific call to action. Even if a poster has a call to action it is not unusual to see a movie poster or a poster for an event or play to be hanging on someone’s wall for years, often framed. it is not unreasonable to think that a poster can be more than a superficial message. We can expect there to be something in the design which requires the viewer to bring something to it, like we expect in a painting.
Many things in my life are not in the common experience, that does not make me better or worse, smarter or dumber,or whatever, its just my own interest. And these posters are like a simple book expressing something simply about a personal interest.