gistfile1.php

if($file = $page->file('header.png')) { 
      echo ' hasimage" style="background-image:url(' . $file->url() . ');' ; 
} else {
      foreach($site->children()->visible() as $item) {
            if ($page->isDescendantOf($item) && $file = $item->file('header.png')) {
                  echo ' hasimage" style="background-image:url(' . $file->url() . ');' ;
            }
      };
}