iCloud: Photos overview
iCloud lets you share your favorite moments with your favorite people when you create a shared photo stream. Friends and family you invite to share your streams can post their own photos, videos, and comments, and changes appear automatically on everyone’s devices. You can quickly and easily see the latest updates from all your shared streams in the Activity view on your device.
iCloud also stores all your photos recently added to your devices in My Photo Stream. It’s a great way to get all your latest shots on all your personal devices.
My Photo Stream and iCloud Photo Sharing are designed to allow you to upload as many photos and videos as you want. However, to prevent unintended or excessive use, iCloud limits the number of items that can be uploaded within a given hour, day, or month. For more information, see the Apple Support article iCloud: My Photo Stream and iCloud Photo Sharing limits.