I recently uploaded an epub book that is mostly photographic images.https://www.gaytorrent.ru/details.php?id=1d7f2a297d98f635b9f5b89e8d356c2cbfa717d2b9028eab
I made a comment explaining how you can extract the images from an epub file but I thought I should post the information here in case people don't know.
.epub, like .docx, .xlsx etc. are actually zip archives with a directory structure containing xml and content. So you can easily hack into them by adding the extension .zip (if necessary) and then using your unzip utility to expand it. For epubs like the Marcelino nude photography book I linked to above, you would find in the expanded epub/zip a directory called "images" containing all the images linked to in the book.