You might do it via a Servlet (ok, probably not the best solution *G*):

public class GetMeTheImagesServlet extends HttpServlet {

 // ...

 public void processRequest(HttpServletRequest req, HttpServletResponse res) {
 String dir = getServletConfig().getInitParameter("ROOT_DIR");
 String file = req.getParameter("FILENAME");
 String filename = dir + "/" + file;

 // create a FileInputStream and

 PrintWriter out = response.getWriter();
 response.setContentType("text/text;charset=UTF-8");

 // create a FileInputStream for filename and pipe the bytes to out

 out.close();
 }

 // ...

}