Quote:
Originally Posted by Hitch
I'm sure you're right on that. I just never noticed, LOL! I guess, though, in looking at the technical side, that enormous fortune could afford the additional costs of individualized watermarking. I can't imagine anyone else's books, ever, really, being that popular or having that much profit in them. (To pay for that type of watermarking cost.)
Hitch
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I expect it's super easy and cheap to do (probably just like adding serial numbers and something even Calibre can do easily). The watermark/hash isn't literally invisible. If you extract the epub (simple zip file) and view the underlying HTML with a simple text editor, you'll see the watermark/hash. It's just not visible when reading the ebooks via epub reader.
I believe comiXology does something similar for their DRM-free comics backups (granted, embedded in image files).