Through my recent travels I've regularly been waking up to a fully-charged iPhone warning me it couldn't back up because I don't have enough free space with iCloud.
With 25GB of iCloud storage this has never before been an issue, at least not before I enabled iCloud Photo Library. I like it, in theory, but with other, free cloud photo storage solutions iCloud Photo Library just doesn't make sense for me to buy online storage. I like the syncing offered by PhotoStream, but I've found that's all I really need.
Disabling iCloud Photo Library to reclaim my storage seemed like a simple task, but turns out disabling it without losing any of one's photos in the process is not so simple.
Here are the steps to disable iCloud Photo Library without losing any of your data. You will be using all of your iOS devices for this but only one of your Macs. That Mac, in the end, will wind up as the main repository for all of your photos:
First things first, convert to Photos on your Mac. iPhoto is great, but the future is Photos.
Once you're using Photos, disable iCloud Photo Library on your Mac by going into Photos > Preferences > iCloud and uncheck iCloud Photo Library. If you don't do this then you'll continually be uploading your photos to iCloud during the rest of this process, perpetuating the problem.
On your Mac, import each of your iOS devices' photos into the Photos app. To do this, connect your iOS device to your Mac via USB, go into Photos, select your device and click the "Import All New Items" button. This will ensure you have everything from all your devices on your Mac. Again, be sure to repeat this process with each of your iOS devices.
Import All New Items from your iOS devices to be sure not to lose anything.
Once you've done this, go to each of your iOS devices and disable iCloud Photo Library. This is done in Settings > iCloud > Photos and disable iCloud Photo Library. You can leave everything else there, including My Photo Stream enabled if you like.
At this point your Mac's Photos Library will have everything that was on each of your devices. It's possible this means you have everything, but that's not a guarantee because of the way iCloud Photo Library manages space on your iOS devices. Sometimes your iOS devices may wind up with lower resolution versions of your photos and you want to make sure you keep the highest resolution version possible. The next step, therefore, is to download all your photos directly from iCloud Photo Library on the web.
Because iCloud Photo Library will download each and every photo as a separate file, you will want to first disable Safari's "Open Safe Files" option. Do this on your Mac by going into Safari > Preferences > General and uncheck the "Open 'safe' files after downloading" checkbox. If you don't then the next step will open thousands of photos in Preview, bogging down your Mac. You may also want to temporarily set a different downloads folder for Safari just to keep things clean. This is done in the same window with the "File download location" dropdown.
With Safari properly configured, visit iCloud.com/#photos, click "Select Photos" at the top of the screen, then select all of your photos by clicking the very first one and then scrolling down to the bottom and shift-clicking the very last one. Once selected, choose "Download" at the top of the screen. This may take a little while.
Using iCloud Photo Library's web interface you can select, download and delete your photos.
Once all the photos are downloaded, simply use the Finder and drag them all at once into Photos on your Mac. Photos may ask if you want to skip duplicates (let it) and will import everything else. Doing this allows you to be absolutely certain that everything you have in iCloud Photo Library now lives on your Mac.
With that complete, go back to iCloud Photo Library in Safari, select all your photos again and this time choose "Delete". They'll stay in the iCloud Photo Library trash for at least 30 days in case you made a mistake.
Now that your iOS devices aren't using iCloud Photo Library they'll default (back) to backing up your photos as part of your normal iCloud backups, something many of us had previously disabled. You may want to re-disable this by going into Settings > iCloud > Storage > Manage Storage > [This Device] on each of your iOS devices and disabled the slider next to Photo Library.
At this point you're finished, but my advice is to sign up for a free, 1TB storage Flickr account and then run Flickr Uploadr for Mac to backup your photos to the cloud. Your photos will be stored on Flickr privately until you go online and change the status individually.
iCloud Photo Library is a great idea, and for some it will work perfectly. For the rest of us, we now have the steps to unravel it without losing data.