static NanoHTTPD.Response servePNG(BufferedImage img) {
  ret serveByteArray(toPNG(img), pngMimeType());
}

static NanoHTTPD.Response servePNG(File file) {
  ret serveFile(file, pngMimeType());
}

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

Began life as a copy of #1011249