protected function encode($fieldsDef, $modelSection)
 {
     $encoded = '';
     foreach ($fieldsDef as $field => $definition) {
         if (isset($modelSection->{$field})) {
             $format = $definition['picture'];
             $encoded .= Picture::encode($modelSection->{$field}, $format, array('field_desc' => $field));
         }
     }
     return $encoded;
 }