title: Add mask to camera
body: <p>I am new on Flutter and trying to do an app that use camera. So, everything works fine and I am using <strong>image_picker</strong> lib. Now, I need to add a mask for my user to capture using this mask to position the document (like a overlay) but I can't find anywhere saying how to do that. Does anyone know if it's possible using this lib to do it?</p>
  
  <p>Regards,</p>