In the beginning, Hollywood and its movies had a shady reputation. Hence their movie posters often showed an image of the book on which a movie script was based. They imagined the picture of a book would imply a certain cultural quality in the film and would in turn raise its prestige and profits.
Today, books shown in movie posters are generally used to cover up or obscure other parts of the poster. And many books today are written in the hope that they will one day become movie scripts—increasing the prestige and profit of the writer and publisher.
Another interesting trend today is the appearance of the book image on book covers themselves. Sometimes, for obvious reasons, an image of the book is used on a cover if the plot involves a library or a bookshop, or if the book is actually about books. But at other times, the reasons are not so obvious. It may be the publishers were thinking that an image of a book on a book cover would guarantee a certain cultural quality in the book and would in turn raise its prestige and profits.
It would be interesting if, one day, one of these books with an image of a book on its cover were turned into a movie. Then we might see a movie poster with an image of a book that has an image of a book on its cover.