Duplicate photos from Photos?

I can also recommend Photos Duplicate Cleaner. It is free, but will prompt you to upgrade to the paid version.

https://www.duplicatephotosfixer.com/photocleaner

When I tested it, it grouped the duplicates like Photo Sweeper I an overview for comparison and inspection, and could automatically mark candidates for deletion. The marked photos will be added to an album, so we can safely delete them from this album using the Photos.app. It is safe to use and free, but both PowerPhotos and Photo Sweeper are more convenient . And one problem I noticed is, that the thumbnails of the photos are not showing the edited version, but the original. So we cannot be sure, if we are deleting the edited version or the original.

Hi

An app designed to work with the photos library (Ie one that marks the photos or puts them in an album, and lets you review and then delete them, rather than doing the delete itself.

Do NOT use a general file duplicate finder not designed to work with the photos library. They will damage your photos library and likely cause loss of your photos.

I personally use PowerPhotos (I also use this for copying images and data between libraries)
https://www.fatcatsoftware.com/powerphotos/


Another suitable app recommended by experts here is PhotoSweeper (I have no personal experience of this one)

https://overmacs.com/

Both are paid apps. PhotoSweeper is the lowest cost, but PowerPhotos provides a lot of functionality in addition to the duplicate detection.