A complete-looking Photos library can include items whose full-resolution originals are stored in iCloud. That is normal when storage optimisation is enabled, but it matters before you erase a Mac, change storage or make a separate archive.

Check the library's storage choice

Open Photos, then its Settings or Preferences and the iCloud section. Apple distinguishes Optimise Mac Storage from Download Originals to this Mac. Optimisation can retain smaller local versions when space is needed; downloading originals keeps full-resolution material on the Mac as well as in iCloud.

Before changing that setting, compare the library's needs with available storage. A large collection may take substantial time and space to download. Do not start this immediately before wiping the machine or leaving an internet connection.

Check the library's status and allow outstanding work to finish. Seeing a familiar thumbnail is not a verification that every video and original image has completed downloading.

Verify the independent copy

For a preservation task, decide whether you need the complete Photos library, exported original media, or both. The library preserves an application-managed organisation; an export serves a different purpose. Record which result you intend to keep so that albums or edits are not silently excluded from your expectations.

Open samples from the actual backup or exported destination, including older images, recent images and videos. For an offline-original check, disconnect from the network temporarily and inspect material that was not recently opened.

Apple advises keeping backup copies of an iCloud Photos library. Treat synchronisation and backup as separate responsibilities. A second device showing the same collection does not, by itself, prove there is an independent copy with the recovery history you need.

Only proceed with the planned erase or storage change once the intended originals and organisational information have been preserved and checked.

Sources: Apple's iCloud Photos guide and Photos storage settings.

For help with your Mac, contact AEPC in East Auckland or call 027 908 8880 to discuss your requirements.