title: ARCore Extended ImageTracking / Anchoring API in Unity
body: <p>The ARCore AugmentedImage example application that comes with the Unity SDK package places a picture frame around the sample images included in the sample AugmentedImageDatabase. It will place a picture frame around multiple images in the scene if they are found, and only destroy the picture frames once tracking is lost entirely. </p>
  
  <p>Suppose you wanted to only display a picture frame around the image most recently recognized - and remove the frame from the previous image? Checking the TrackingState of a given image doesn't help since the tracking is extended by default without any way to turn off, and the anchor API doesn't offer any information that would help either.</p>
  
  <p>I have it working by destroying the old session (and creating a new one) once the list that holds the Trackable images exceeds 1, but that leads to the app temporarily freezing up for a second before resuming.</p>
  
  <p>Are there suggestions on a better way to do this?</p>