static NanoHTTPD.Response serveJPEG(BufferedImage img) {
  ret serveByteArray(toJPG(img), jpegMimeType());
}

static NanoHTTPD.Response serveJPEG(File file) {
  ret serveFile(file, jpegMimeType());
}

static NanoHTTPD.Response serveJPEG(byte[] imgData) {
  ret serveByteArray(imgData, jpegMimeType());
}