best way to remove photo duplicates

Always have a redundant backup plan in place before attempting to use third party apps in the event you have to recover.

https://discussions.apple.com/docs/DOC-10081

—Using third-party apps to remove duplicate photos might damage your Photos for macOS library - Apple Support

— Removing duplicate photos.

The Apple Support document you just read is a bit vague, and does not tell directly, which duplicate cleaners are dangerous.

You have to stay clear of all cleaning applications that will directly remove files from your Photos Library. This can damage the library. Use only the cleaning applications, that are using the Photos scripting interface to add duplicates to an album. And then you can review this album and delete the duplicates using Photos.

I have tested PowerPhotos, Photo Sweeper, and Duplicate Annihilator and found them safe to use. The trial versions of CleanMyMac 2 and 3 damaged my Photos library and caused data loss.

It will depend on the kind of duplicates which application will be best for your purpose.

• PowerPhotos is the current swiss army knife as a companion for Photos and can help with many Photos related tasks. It will find exact duplicates based on the file attributes - filename or date.
• Photo Sweeper does not only compare the file attributes, but compares the histograms and bitmaps of the photos. It is able to find duplicates of the same photo. if the file has been edited or downsized.

So, which kind of duplicates do you need to find?