Barely-amusing image aside, used ebooks are for real. Or at least have a very real potential to become real. See, Amazon just cleared a patent for technology that would allow it to create an online marketplace for used ebooks--essentially, if you own an ebook, you would theoretically be able to put it up for sale on a secondary market.
The approved patent describes the process:
Digital objects including e-books, audio, video, computer applications, etc., purchased from an original vendor by a user are stored in a user's personalized data store
Link to Original Source