I've been going through bookshelves at the University of Helsinki in search for course books that have been in use for a good while.
When I've found books that look suitably scruffy and used, I go through several copies of the same book, looking for pages, in common for all copies, that have collected underlinings, jottings and marker pen highlightings in a visually interesting way.
Then, after photographing this one active page from several copies of the same book, I have removed the printed text and combined the images as one. Usually one image consists of three to five pages.
This way, I get a collection of visible markings in the image. These markings are signs of studies.