code: public function verticalFlip( $region = null )
      {
          $resource = $this->getActiveResource();
  
          $w = imagesx( $resource );
          $h = imagesy( $resource );
  
          $newResource = imagecreatetruecolor( $w, $h );
  
          imagealphablending( $newResource, false );
          imagesavealpha( $newResource, true );
  
          $res = imagecopyresampled( $newResource, $resource,
              0, 0,
              0, $h,
              $w, $h,
              $w, - $h );
  
          if ( $res === false )
          {
              throw new ezcImageFilterFailedException( 'rotate', 'Rotation of image failed.' );
          }
  
          imagedestroy( $resource );
          $this->setActiveResource( $newResource );
      }
docs: /* (non-PHPdoc)
  @see extension/ezie/autoloads/eziezc/interfaces/eZIEEzcConversions#verticalFlip($region)