def image_server_response(self, api_version=None):
        """Response, code and headers for image server error response.

        api_version selects the format (XML of 1.0). The return value is
        a tuple of
          response - body of HTTP response
          status - the HTTP status code
          headers - a dict of HTTP headers which will include the Content-Type

        As a side effect the routine sets self.content_type
        to the correct media type for the response.
        """
        headers = dict(self.headers)
        if (api_version < '1.1'):
            headers['Content-Type'] = 'text/xml'
            response = self.as_xml()
        else:
            headers['Content-Type'] = 'text/plain'
            response = self.as_txt()
        return(response, self.code, headers)