Background: single image
In Delight you can decide a general background for the entire site, but also a different background in any page (this option overwrites the previous, of course).
In this case you can see a single image as background. It is very simple to set.
If you want that all your pages have a single image as background, just set the default background in the Delight Admin Panel:
If you want to apply a particular image to one page only, a custom box in the page itself allows it: