Photos for OSX. Duplicates.

So I can more or less safely delete duplicates that are found with my 3rd party app without fear of deleting any photos from albums then?

It depends on the 3rd party app you are using to detect and remove duplicates. Only some of them are safe to use. If the app is modifying your Photos Library and not just collecting the duplicates in an album for you to move to the Recently Deleted album, the app may destroy your library beyond repair. See Apple's warning: Using third-party apps to remove duplicate photos might damage your Photos for macOS library - Apple Support

Some third-party apps for your Mac that claim to clean, shrink, de-clutter, or remove duplicates from Photos can instead damage your photo library or delete pictures and related data.

I found these three duplicate detectors safe to use. They are working well on my Photos library, even with iCloud, but have not tested all available third party apps.

• Power Photos
• Photo Sweeper
• Duplicate Annihilator

without fear of deleting any photos from albums then?

If you delete a photo from your library, it will vanish from all albums you added it to. The albums are using the photos in the library and not storing duplicates. A photo is only a duplicate in your library, if you are seeing the photo twice in the moments, which are showing the photos in the library. Even if you are using "Image > Duplicate" in Photos, the original image file will only be stored once in your library. Photos is just creating a second version of the image, and the versions will share the same original.

there are no events in Photos

When you migrate your iPhoto events are converted into albums and stored in a folder named iPhoto events

You can not possibly create an event in Photo - you can create an album with event in the name but it is just an album and like all albums nothiong is a duplicate - albums are one of several ways to view photos - they are not a place to "put" photos as they do not exist except virutally

LN

I am using 3rd party software to detect duplicates in Apple Photos.

Which program are you using? Some duplicate detectors are showing duplicates that are no duplicates but similar looking photos

1. photos you edited or pairs of thumbnails and the original. if you have edited your photos, most of them will show as duplicates. You will want to keep both the original and the edited version
2. Or if you took photos in quick succession, you may have many nearly identical photos that are no duplicates. You have to compare them visually to keep theist shot.
3. You may have downsized versions of your photos, if you used My Photo stream or Shared albums. Then the full sized original and the shared smaller version may be in your library and you have to compare the pixel sizes to pick the better quality version.

I have thousands of duplicates which is strange.

What kind of duplicates are these? Are you seeing the same photo several times in the Moments - with an identical file size and an identical filename? Only if the photo is more than once in the moments, it is a duplicate. But If the same photo appears in three different albums, it is not a duplicate. You have only used it in more than one album.

Could these have somehow been created when I migrated from iPhoto to Photos?

The Photos Migration does not create duplicates, but it may be showing you the edited version and the original as two photos.

If you see a photo twice in the moments, but only one of the versions is in an album, and you want to keep it in the album, drag both versions from the moments to the album. Then delete the version from the moments, that you do not want to keep, usually the

I don't think that's a "true" duplicate: the photo is stored in the main library, and an instance of it is shown in the event, but the file itself isn't duplicated. This is the way Photos works with albums too.