Add background to a div based on a Node's Image Field
You could try BackgroundField:


  BackgroundField started as an extension of the CCK ImageField that
  allows a CSS selector and background attributes to be set for a
  content-type. This is particularly helpful for allowing your node
  authors to add images to a node that are integrated into the theme of
  the site. With the inclusion of the Image field in Drupal 7,
  BackgroundField was rewritten to extend that core functionality.