This week's book giveaway is in the OCMJEA forum. We're giving away four copies of OCM Java EE 6 Enterprise Architect Exam Guide and have Paul Allen & Joseph Bambara on-line! See this thread for details.
You can only have one content type, text or image. The text (or rather, HTML) can contain an image that once again references the servlet so that it serves an image; but that would be a separate follow-up request.