class Page extends SiteTree {

   static $has_one = array(
      'BannerImage' => 'Page_BannerImage'
   );
   
   function getBannerImageRecursive() {
      $page = $this;
      $banner = $this->BannerImage();
      while(!$banner->ID && $page->ParentID != 0) {
         $page = $page->Parent();
         $banner = $page->BannerImage();
      }
      return $banner;
   }
   
   function getCMSFields() {
   $fields = parent::getCMSFields();   
   $fields->addFieldToTab('Root.Content.Header', new ImageField('BannerImage', 'Banner'));
   
   return $fields;
   }

}

class Page_BannerImage extends Image {
   
   function generateFullWidth($gd) {
      $gd->setQuality(80);
      return $gd->croppedResize(934,267);
   }

}