code: def _create_thumbnail(self, source_image, geometry_string, options,
                            thumbnail):
          
          logger.debug('Creating thumbnail file [%s] at [%s] with [%s]',
                       thumbnail.name, geometry_string, options)
          ratio = default.engine.get_image_ratio(source_image, options)
          geometry = parse_geometry(geometry_string, ratio)
          image = default.engine.create(source_image, geometry, options)
          default.engine.write(image, options, thumbnail)
          # It's much cheaper to set the size here
          size = default.engine.get_image_size(image)
          thumbnail.set_size(size)
docs: Creates the thumbnail by using default.engine