I downloaded the macOS Sierra (GM) and installed it on my MacBook. Before I installed it a backed up all my data that isn't stored in the cloud or somewhere else.

I'm using iCloud Photos to sync all my photos and videos with iCloud. Every photo and video is already in iCloud so I may don't need to back up my Photos library, but I did - just in case something goes wrong.

So I wiped off all the data from my MacBook to do a complete and clean installation of Sierra. Finally everything works fine and I'm going to get all my photos and videos back to the Photos app.

My backup of my photos and videos has ~13GB and I really have a slow internet connection, so it would be nice if I could use the backed up library instead of downloading everything from iCloud.

As soon as I open my library with Photos it starts importing and optimizing etc. and all photos and videos are there. But it starts uploading every single photo and video to iCloud? How can I tell Photos that my photos and videos are already in iCloud and it should stop uploading?

  • It may say it's going to upload them, but I believe it will figure out that they're matches before it actually uploads.
    – tubedogg
    Sep 17, 2016 at 23:09
  • I think you are right, it stopped after some time and didn't upload any more ..
    – beeef
    Sep 17, 2016 at 23:44

2 Answers 2


The Photos app in macOS Sierra is able to do a comparison between what is in the cloud, and what is stored in the local library on your Mac. (Likely through some means of signature/hash function).

To provide some insight with actual numbers - My Photos library is approximately 53GB, and only required about ~1.5GB worth of bandwidth to validate/sync the library after migrating the library to a different Mac with a fresh install of macOS Sierra (1.5GB includes any photos that it also needed to sync since the last my library was active).

With that being said, you can be confident that your bandwidth limitation, or capacity, should not have to handle the full file size. However, be mindful that if there are other cloud services (iCloud Drive) they too can utilize bandwidth.


The correct way is exactly as you did it. Photos.app should determine that the photos are identical to the ones already in the cloud. A limited amount of data may be used to accomplish this, but it should not use anywhere near the size of your whole library.

  • How does Apple do this? You have to upload a photo to check if that photo is already in the cloud. Does the Photos app upload compressed images to do a match?
    – beeef
    Sep 18, 2016 at 7:52
  • I don't know for absolute certain in Photos' case, but my guess is they create an image signature that uniquely identifies each image, uploads those and compares them. The whole image doesn't need to be uploaded.
    – tubedogg
    Sep 18, 2016 at 15:24
  • It still says "Uploading 1600 elements" .. my internet is totally blocked because of the continuous uploading. I now paused the uploading in the Photos.app and internet is working fine now. That's really a tragedy with "only" 13GBs of photos and videos ..
    – beeef
    Sep 18, 2016 at 15:30

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