Resizes and saves the thumbnail image

def _create_thumbnail(self, model_instance, thumbnail, image_name):
        """
        Resizes and saves the thumbnail image
        """
        thumbnail = self._do_resize(thumbnail, self.thumbnail_size)
        full_image_name = self.generate_filename(model_instance, image_name)
        thumbnail_filename = _get_thumbnail_filename(full_image_name)
        thumb = self._get_simple_uploaded_file(thumbnail, thumbnail_filename)
        self.storage.save(thumbnail_filename, thumb)