Understanding photo storage and syncing

If you turn on iCloud Photo Library in Settings > Photos (iOS) and Photos > Preferences > iCloud (Mac), your existing and future photos are uploaded to Apple’s server until your iCloud storage fills up.

On one Mac, it’s a good idea to choose ‘Download Originals to this Mac’ to keep a local copy of the full-quality originals. From this, make a full, offline backup regularly.

iCloud Photo Library not syncing? Go to Photos’ preferences (Mac) or the app’s Photos tab (iOS) and check you haven’t paused it and forgotten. Otherwise, the simple old trick of turning it off and on again (after a few minutes) can kick-start it into action.