See http://www.tersus.com/#Tag=Image for links to pages explaining the different methods which can be used.
For static images we've added the option to drag an image file from the desktop and drop it into the studio model editor, which should do all of the following automatically:
Stefen is right in that background images are implemented via CSS. See http://www.tersus.com/#Tag=CSS for information on using CSS in Tersus.
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