Reading bookshelf contents using RFID tags on books
You could also use machine vision + AI to detect what books are there, based on the writing on the spine. If they're tagged with an ISBN number, even better.
That's basically what Amazon Go does, but with a wider set of items. Your problem set is simpler, since you’re only recognizing books and text.
Using a visual method has the additional bonus of showing the location of the book, something RFID cannot do, realistically.