Can I merge two photo libraries?

With PowerPhotos you have these options in merging one library into another:

Also copied will be the metadata including keywords, descriptions, titles, dates, and favorite status.

When I've done it I've picked the smaller library with fewer projects to copy into the larger of the two libraries. Also make sure you have current backups of the libraries just in case.

The iCloud Library method is a more complete merge but will take longer and you'll have to purchase enough iCloud Drive space to hold the merged libraries.

PowerPhotos has a demo version which will do everything except merge libraries and search for duplicates.

Merging in iCloud is the only way to merge the two libraries while preserving the lossless workflow and keeping the originals and edited versions paired so you can revert to the original.

It would have been easier to do all merging of libraries while you still could use Aperture to merge libraries.

Photos has no tools to merge libraries other than in iCloud.

Set each as the System Photo Library and upload it to the iCloud(you may need to pay for additional storage), or use PowerPhotos to merge them.

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