let observer = ScreenShotObserver()
observer.rx.image
  .subscribe(onNext: { image in
    // Add / Update / Remove events images
  })

observer.rx.item
  .subscribe(onNext: { item in
    // Add / Update / Remove events NSMetadataItem
  })

observer.rx.addedImage
  .subscribe(onNext: { image in
    // Add events image
  })

observer.rx.updatedImage
  .subscribe(onNext: { image in
    // Update events image
  })

observer.rx.removedImage
  .subscribe(onNext: { image in
    // Remove events image
  })
observer.start()