/**
  * this function loads the thumbnail image for the challenge identity
  */
 public function actionIcon()
 {
     $challenge = get_entity($this->url_vars[1]);
     $size = $this->url_vars[2];
     $image_name = 'contest/' . $challenge->guid . '/icon' . ($size ? $size : 'small') . '.jpg';
     $content = IzapBase::getFile(array('source' => $image_name, 'owner_guid' => $challenge->owner_guid));
     if (empty($content)) {
         $content = file_get_contents(elgg_get_plugins_path() . GLOBAL_IZAP_ELGG_BRIDGE . '/_graphics/no-image-' . $size . '.jpg');
     }
     $header_array = array();
     $header_array['content_type'] = 'image/jpeg';
     $header_array['file_name'] = elgg_get_friendly_title($challenge->title);
     IzapBase::cacheHeaders($header_array);
     echo $content;
 }