title: Classify faces from VNFaceObservation
body: <p>I'm working with <code>Vision</code> framework to detect faces and objects on multiple images and works fantastic.</p>
  
  <p>But I have a question that I can't find on documentation. The Photos app on iOS classify faces and you can click on face and show all the images with this face. </p>
  
  <p>How can I classify faces like Photos app? Is there any unique identifier or similar to do this?</p>
  
  <p>Thanks!</p>