What is iCloud Photo Library?
Your complete collection of photos, available on all of your devices
Although you can use Photos in isolation on your Mac, it becomes something special when you connect it to iCloud.
The point of iCloud Photo Library is that you shouldn’t have to concern yourself with which device you used to take a photo, or into which one’s library you imported some pictures; every photo is available to download and edit on any and all of your devices. Photos, and videos too, are automatically uploaded to your online library at their full quality, editing decisions are replicated across all of your devices, and you can roll them back on any device as well.
You need to consider the implications of free space dwindling on your devices and in iCloud. On the iCloud side, Apple’s simplest solution is to offer you additional storage beyond the 5GB it provides for free, ranging from 79p for 50GB to £6.99 for 1TB per month. Whichever tier you pick, bear in mind that the space is shared with other iCloud features, notably email and iCloud Drive. If you aren’t willing to pay for as much space as it takes to store your entire library online, you can fall back on Photos’ ability to work with multiple libraries and be selective about what’s uploaded. You’ll need to be content to work in a more old-fashioned way, switching to the appropriate library, and manually import photos and videos from your camera to your Mac.
When it comes to local storage, Photos has a setting, which is applied on a per-device basis, that determines whether a device stores the full-quality originals of all photos, if it has room, or versions that are optimised for it. With