Notes on Merging Photos Libraries, 2019 Version
When merging two photo libraries we usually want a lossless merge:
- The original photos and the edited versions should be merged into the merged library as master-version pairs, so it will be possible to revert edited photos to the original.
- The library structure with albums, smart albums should be preserved in the merged library.
- All metadata, including the faces labels should be migrated.
- The products (books, cards, calendars, slideshows) should be migrated.
Written for Photos 4.0 on macOS 10.14.4 or older:
(this applies to Photos 5.0 on Catalina as well)
There is currently no completely lossless way to merge Photos Libraries, because Photos does not support importing one Photos Library into another library. All work-around methods are compromises. There is no lossless merging of Photos Libraries other than iCloud Photo Library, and even the merging in iCloud will not include the print products. Photos 2.0 or older will not sync the faces with iCloud.
If you are planning to migrate your photo libraries from Aperture or iPhoto to Photos and own Aperture 3.6, merge your libraries in Aperture before the migration while you still can use Aperture as described here:
Aperture 3.3: How to use Aperture to merge iPhoto libraries (wayback machine)
Make backup copies of the libraries before you try that.
The options in Photos are:
- Merge the libraries in iCloud by uploading them to the same iCloud Photo Library: Merging in iCloud is the only way to preserve the master-version pairs, so you can revert edited photos to the original versions. Your albums and folders will migrate, keywords, titles, and other metadata. All edited images will be paired with their originals, so you can undo the edits and revert to the original. The searchable faces names will upload (only on Photos 1.5 or older, not on Photos 2.0), but not the faces thumbnails and albums. Photos will scan for duplicate original files while merging and resolve conflicts between duplicate originals. It is the best way to migrate libraries you invested much work into, but uploading large libraries to iCloud requires a paid subscription for more storage than the free 5GB - for at least a month, and it is slow. My library with 40000 photos took a full week to upload.
- To merge in iCloud enable the smaller of the two libraries as your iCloud Photo Library.
- Wait for all photos to upload; that can take a very long time, a week ore more, depending on the size of the library. Photos will merge the the library into the library that is already in iCloud.
Now enable the larger library as your iCloud Photo Library. This library will be merged into the library in iCloud too, creating a merged library in iCloud. The merged library will sync back to your larger Photos Library. The merge will not include the Faces albums and projects from the first library you uploaded. That is why I recommend to start with the smaller library. The download will be like to a different Mac, see: Use Photos and iCloud Photos on multiple Mac computers https://discussions.apple.com/docs/DOC-13981
- To sync the faces names with iCloud Photo Library, I apply keywords with the names of the persons to all photos in a people album. Photos 1 and 2 cannot sync the named faces, but Photos 3 and 4 can sync them.
- Merge the libraries by exporting the photos (edited versions and originals) from one library and reimporting them into the other library. (Combine libraries in Photos - Apple Support) This is the most tedious way and only feasible for very small libraries. You would have to export the edited versions and the originals separately and they would no longer be paired. On Yosemite or El Capitan - even if you export the originals with XMP sidecar files to preserve the IPTC metadata, the metadata from the sidecar file will not be applied to the originals when reimporting. Your metadata will be gone, unless you export the edited versions as JPEGS. So there is no help for it but to export both, the originals and the edited versions, and to deal with the duplicates. Photos 2.0 on Sierra can read the sidecar files on import - so exporting with XMP files will transfer the metadata to the new library.
But you will have to recreate the albums and smart albums as well.
- Merge the libraries with PowerPhotos 1.62 or newer: PowerPhotos is a tool to manage Photos Libraries. You can easily browse libraries in turn and move photos and videos between libraries (not bursts). Merging with PowerPhotos is fast (https://www.fatcatsoftware.com/powerphotos/. It will migrate the metadata (but not the faces) and the albums. Fully supported: photos and videos, keeping keywords, descriptions, titles, dates, favorites, locations, bursts, and Live Photos intact; albums, folders, and moments. On older versions of Photos (up to Photos 4 on Mojave) you have to decide, if you want to use the originals or the edited versions. So you will either lose the editing work or the high quality originals or create redundancy by merging twice in two passes, once to transfer the originals, and then the edited versions. You will have to add a pass to remove duplicates afterward. See chapter six in the PowerPhotos manual: : https://www.fatcatsoftware.com/powerphotos/Help/merging%20libraries.html, also: https://www.fatcatsoftware.com/powerphotos/Help/copying%20limitations.html. For older versions of PowerPhotos more limitations apply.
- Another option would by to keep both libraries separate and use PowerPhotos to browse the libraries and to transfer selected albums as you go.
On Mojave, iCloud Photo Library would be the best option. Merging with PowerPhotos the second best. If you are tagging faces in Photos or are using iCloud Photos anyway, I would go for the iCloud merge or upgrade to Catalina, see below.
Update for macOS 12 Monterey or macOS 13 Ventura: If your Mac is running macOS 12 Monterey or macOS 13 Ventura, you can import the photos from your iPhoto Libraries or Photos Libraries into a copy of your largest library on your external drive.
See: Import photos from another library in Photos on Mac – Apple Support (UK)
This will not be a complete merging of the libraries, however. It has some limitations, as the keywords, albums, and folders will not be imported. The merging will avoid duplicates however, and keep the edited versions paired with the originals, when you are importing from a Photos Library. And when importing from an iPhoto Library only the originals will be imported. Only importing from a Photos Library will save the edited versions. So you may want to convert any remaining iPhoto Libraries to Photos Libraries.
Update for PowerPhotos Version: 1.7.7 on Catalina macOS10.15.2
PowerPhotos now supports a nearly lossless merging of libraries and exporting partial libraries, including the locations, videos, Live Photos. There are still a few limitation for smart albums and named faces. But PowerPhotos now lets us move photos between libraries as master-version pair with reversible edits. Live Photos are also supported. See the updated feature list:
https://www.fatcatsoftware.com/powerphotos/Docs/copying_limitations.html
And the limitations when merging into an iCloud Photos Library:
https://www.fatcatsoftware.com/powerphotos/Docs/copying_icloud.html
Update for Photos 3.0 on macOS 10.13 and Photos 4.0 on macOS 10.14 Mojave:
Photos 3.0 and Photos 4.0 will also sync the recognized faces when you merge two Photos libraries in iCloud. Projects do still not sync to iCloud.
Old deprecated version: Notes on Merging Photos Libraries - Apple Community