Where are our iCloud images stored? My wife and I recently changed to Apple. Our setup includes a Macbook Pro, Apple TV and two iPhones. I have purchased 2 TB of iCloud storage which I am sharing with my wife. 

We have ~3000 high-rez images that we want to migrate into iCloud Photos. They are stored on a Dropbox account today, so I installed iCloud for Windows on our old PC and started adding the images to shared albums in iCloud photos. 

After quite some time, it seems like they are all uploaded and we can view them on all devices. 

Now, here's the thing I can't wrap my head around. Even though it's about 12 GB of images that we've uploaded so far, iCloud still says we only consume 1 GB of disk space, and on my iPhone, the internal disk space says "~180 MB images" and "~5 GB other". The "other" part came when I started syncing images. 

On my phone I have both iCloud-images and Optimize iPhone storage enabled. I though this would mean that the images where saved in their original resolution in iCloud, and at a lower kind of "preview" resolution on our phones, but since iCloud usage is not incrementing I guess I have understood it wrong. 

The All images folder on my device is empty, but the shared albums folders are full of images. Shouldn't the disk usage on iCloud reflect that?

We're a bit worried that we have done something wrong and that our images might be deleted by mistake. Hence, here's a few questions that you'll hopefully be able to answer for us:


Are our images uploaded to iCloud and not stored locally on my phone?
If they are uploaded into iCloud, how come we don't see an increase in disk usage? Why should one pay for additional iCloud storage when it doesn't increase?
What happens if I reinstall my phone? Will our images still be left "intact" in iCloud and ready to be synced once the phone is back up and running?
Is iCloud photos sufficient as a backup solution for the images? Or is it recommended to use an additional backup (I mean, more backups is always better, but is it overkill?)
The reason this seems confusing is that you've added the photos to "Shared albums".

Usually you would add your own photos to the Photos Library, which is essentially meant to be a collection of all your photos. Compared to that, "Shared Albums" is meant for taking out smaller collections of photos that you want to shared with third parties. 

Photos added to your own Photos Library do count against your iCloud storage limit, however photos added to shared albums do not. This is why you're not seeing any increase in your usage of iCloud. Shared albums comes with a built-in limitation of 5000 photos per album.

You can read more about iCloud Shared Albums storage restrictions here:

https://support.apple.com/en-us/HT202786

When you add a photo to a shared album, or to the Photos Library, the photos are uploaded to iCloud, yes. Whether or not they're also stored locally on your phone depends on your settings and how much storage space you have. You can choose to "Optimize storage", which means that only some is keps in full resolution on your phone, as space permits, otherwise only low res versions are kept on the device. The full res versions will be fetched from iCloud on request.

If you reinstall your phone, nothing happens to the iCloud stored photos. They will all be intact and ready to be synced after the phone is back up and running. However, note that you will need to be able to login with your Apple-ID (i.e. remember email-address, password and 2FA device if applicable).

Whether or not this is sufficient as a backup solution is up to you. If it were me, I wouldn't say it is sufficient - I would always keep photos stored in a minimum of two systems. With iCloud Photos you can setup your devices so that the full res images are stored both in iCloud and on a local device. This leaves you with 2 copies... however a single error (user error or bug) could erase your photos from both places at the same time. That's why I always recommend a second backup.