/**
  * Returns an object to be used by `json_encode` to serialize objects of this class.
  *
  * @return object
  *
  * @see http://php.net/manual/en/jsonserializable.jsonserialize.php JsonSerializable::jsonSerialize
  *
  * @api
  */
 public function jsonSerialize()
 {
     $obj = parent::jsonSerialize();
     $obj->details->image = (object) ['width' => $this->width, 'height' => $this->height];
     return $obj;
 }