def _render_image(self, spec, container_args, alt_text=None):
        """ Render an image specification into an <img> tag """

        try:
            path, image_args, title = image.parse_image_spec(spec)
        except Exception as err:  # pylint: disable=broad-except
            logger.exception("Got error on spec %s: %s", spec, err)
            return ('<span class="error">Couldn\'t parse image spec: ' +
                    '<code>{}</code> {}</span>'.format(flask.escape(spec),
                                                       flask.escape(str(err))))

        composite_args = {**container_args, **image_args}

        try:
            img = image.get_image(path, self._search_path)
        except Exception as err:  # pylint: disable=broad-except
            logger.exception("Got error on image %s: %s", path, err)
            return ('<span class="error">Error loading image {}: {}</span>'.format(
                flask.escape(spec), flask.escape(str(err))))

        return img.get_img_tag(title, alt_text, **composite_args)
Render an image specification into an <img> tag