response.addHeader("Pragma", "No-cache");
response.addHeader("Expires", RFC822_FORMAT.format(Calendar.getInstance().getTime()));
String resource = request.getRequestURI();
String extension = resource.substring(resource.lastIndexOf('.') + 1).toLowerCase();
if (extension.equals("jpg") || extension.equals("png")) {
BufferedImage image = captcha.generateImage();
response.setContentType("image/" + extension);
ImageIO.write(image, extension, response.getOutputStream());
} else {
BufferedImage image = captcha.generateImage();
response.setContentType("image/png");