iCloud: iCloud Photo Library overview
You can use iCloud Photo Library to automatically upload your photos and videos to iCloud, so you can access them from your iPhone, iPad, iPod touch, Apple TV, Mac, Windows computer, and iCloud.com. Because iCloud Photo Library keeps your originals in iCloud, you can choose to keep smaller versions on your devices to save space. When you add or edit a photo on an iOS device or a Mac, the new or changed photo appears on all your iOS devices, on your Mac, and on iCloud.com when signed in using the same Apple ID.
iCloud Photo Library also keeps track of any organizational improvements you make to your photo library. You’ll always see the latest versions of your photos, videos, and albums, on every device.
Your iCloud account provides 5 GB of free storage space, which is used for iCloud Photo Library (as well as your other iCloud storage needs). As your photo library grows, you can upgrade your storage space as needed. Using iCloud Photo Library gives you the assurance that your photos are stored independently from the other information on your computers and devices. Once you set up iCloud Photo Library, all your photos and videos are automatically uploaded to iCloud via a Wi-Fi or Ethernet connection.
System requirements
For iCloud Photo Library system requirements, see the Apple Support article System requirements for iCloud.
Photo and video files are often large. Photos and videos are only uploaded to iCloud Photo Library when your iOS device, Mac, or Windows computer is connected using Wi-Fi or Ethernet. For best results, also use Wi-Fi or Ethernet (with a broadband Internet connection) to download your photos and videos from iCloud Photo Library.