Background Image
From SAP Enable Now Wiki
Scope
Purpose
This property can be used to select an image to display behind the Book Page in the Book Reader (as an alternative to using a Background Color). Note that this will be scaled to fit the full width or height of the browser window content area, so you should use a suitably-large image.
Not to be confused with the Book Page object Image property, which specifies the image to use as the background of the actual page.