left: Altered book by Jeanette Janson
Old books (but not library books, please) can be turned into works of art with the application of gesso, paint, glue, stamps, paper and found objects of all sorts. Take a look at this site, Make a Mini Altered Book, to view some small altered books with a commentary on how the alteration was achieved. Here is the link to the article "stub" (unfinished article) in Wikipedia about this growing collage phenomenon. BHPL has several excellent books on collage art, altered books and related subjects which will help you start making your own old books into works of art.
Altered art for the first time by Madeline Arendt
Altered art by Terry Taylor
Altered book collage by Barbara Matthiessen
The Complete guide to altered imagery by Karen Michel
If you "google" the phrase "altered book," you will find many websites that explain and show altered books. Here is Eliza Badurina's very clear, concise explanation,
"If you've never heard of an altered book before, the concept is pretty simple: take an existing book and make it into art. Period. End of story.
The long version of the definition, though, is much more complex. There are infinite numbers of things you can do with a book form to turn it into something else. Everything from making "just" an embellished or decorated piece of book art to using the book's form in a new way for a completely different purpose or function. (For example, cutting the "guts" of the book out and turning the empty covers into either another book or, say, a purse or frame -- something you wouldn't normally associate with a book form.) "
My own tip would be to start by using an old child's board book, one that's been chewed and drooled on a bit is perfect. Lift the flaps are fun too. Paint the whole book with gesso or even old white latex house paint to create a new surface to play with. Now start gluing painting.