I like the simplistic shapes which have single colour fills with no shading that express the storyline, on the Wizard of Oz cover, it expressed the three companions of Dorothy in search of a heart, a brain and courage. The heart has been simply reflected horizontally to connote to the Lion’s private parts to symbolise courage. Only simple brown lines changes the meaning of the upside down heart to connote the Lion’s private parts. I think simple things like this makes it clear and concise, however the reader will have to know the story to clearly see what the third symbol means. I think it would make a nice pattern for merchandise too.
The Princess and the Pea is just a simple pattern but the bottom of the pattern has a simple pea. Once again, you would have to know the story to understand what the image is (being loads of beds stacked upon each other). But both covers summarises the story of the contents of the book.