public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        response.setContentType(CONTENT_TYPE);
        OutputStream out = response.getOutputStream();
        JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(out);

        URL url = getServletContext().getResource("/images/symbols.jpg");

        Toolkit kit = Toolkit.getDefaultToolkit();
        ToolkitImage rimage = (ToolkitImage)kit.getImage(url);
        
        if (rimage != null) {
            BufferedImage bi = rimage.getBufferedImage();

            // создаем изображение BufferedImage
            Graphics g = bi.getGraphics();

            // рисуем
            Font fnt = new Font("Arial", Font.PLAIN, 18);
            g.setColor(Color.BLACK);
            g.setFont(fnt);
            
            String txt = String.valueOf(Math.round(Math.random()*10000)).substring(1, 1);
            g.drawString(txt, 10, 20);

            encoder.encode(bi);
        }
        out.close();
    }

BufferedImage bi = rimage.getBufferedImage();