Just seen this link via dictionary.com about fore-edge paintings. These are ‘secret’ paintings made on the sides of books that can be viewed if the pages are slightly fanned apart. I’ve seen other books with fore-edge paintings but this collection of the four seasons on the four books is really delightful.
This is an example of a fore-edge painting on a book called Jerusalem Delivered. This picture was originally from here (the flickr of The Boston Public Library).
I’m now mentally matching up my favourite books with the images I’d like to see hidden on the side of them!