A monthly art theme - explanation here.
A picture book is a story told in words and pictures. Each makes an important contribution to the way the story is told, the meaning created.
A picture is not the same as an illustrated story: there the words alone could tell the story and the illustrations simply break up the words or decorate the text...In the best picture books, the illustrations are absolutely necessary. They carry parts of the story or narrative and in some cases the language is dropped and the pictures alone are all that is needed.
Libby Gleeson. Making Picture Books, 2003. p. 2