first of all exist some flash plugin for read book online, I not know how these will work for mobile devices.
If you give access to some body to some book, you can't restrict for that user do simply screenshot from self monitor.
Ordinary restrict access you may do if will show to users not HTML, if you will show to users PSD or text converted to images(that not restrict from screenshot copy). And for every user that book will have some background water mark, so you will know from who that book move to public access.
As example we created some like that site:
(it yet in development), and there are use PDF, water marks, and user need subscribe for take access to content.
But every time how that will work need special discuss and that will not cheap.