Movie posters have really become works of art. And marketing movies have become an artform as well. In the 50's when filmaking was more about entertainment than substance, they had to market "classics" such as "Attack of the Crab Monsters" by showing a full figured woman being attacked by whatever horrible creature was lurking in the film. There are also some forms of that classic marketing tactic still being used in movie posters today, I am definetly not going to deny that. But I think we have come much further in marketing tactics that film companies can use good visual images rather than the female body all the time. Look at the poster on the left. It is a bold standout image. Its simple and it gets the point across. If you look at the old Jaws movie poster it uses the exact same tactic, simple and clean. Other ways, of course is displaying the stars of movie right on the poster for the "star appeal" factor. The poster from "Anchorman" is a very good example of star appeal.
Movie posters are a prime example of visual communication. Movie posters, as well as the promos, have to be visually appealing otherwise they aren't going to sell any tickets. Posters have to use an image to get the gist of an entire two hour movie.
We have come a long way in the art of movie posters and it's a good thing too. Sometimes thats the only form of art people are going to get.