title: In Dlib how do I save image with overlay?
body: <p>I'm trying to modify Dlib's face detection example to save an image with detections to a file since I'm using a server without GUI. So far I have only figured how to save the image but not the overlay. How do I save both to the same file?</p>
  
  <pre><code>//win.add_overlay(dets, rgb_pixel(255,0,0));
  save_png(img, "detected.png");
  </code></pre>