code: func (p *v1Pusher) lookupImageOnEndpoint(wg *sync.WaitGroup, endpoint string, images chan v1Image, imagesToPush chan string) {
  	defer wg.Done()
  	for image := range images {
  		v1ID := image.V1ID()
  		truncID := stringid.TruncateID(image.Layer().DiffID().String())
  		if err := p.session.LookupRemoteImage(v1ID, endpoint); err != nil {
  			logrus.Errorf("Error in LookupRemoteImage: %s", err)
  			imagesToPush <- v1ID
  			progress.Update(p.config.ProgressOutput, truncID, "Waiting")
  		} else {
  			progress.Update(p.config.ProgressOutput, truncID, "Already exists")
  		}
  	}
  }
docs: // lookupImageOnEndpoint checks the specified endpoint to see if an image exists
  // and if it is absent then it sends the image id to the channel to be pushed.