Metered Pay Wall
variety of PayWall that lets someone read some number of pages for free (in a day? in a month? forever?), then forcing payment (Paid Site) for more/full access.
Typically associated with a Newspaper site, but could work for a Book Server also.
Note that this creates an easier opportunity for a "hacker" to defeat your PayWall, but it's worth it. You'll always have to be seeking Copy Right infringers, even from people scanning Printed Book-s.
Jan'2011 support for the model.
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