Duplicate Photos

It will be a lot easier, if you can wait for the release of macOS 13 Venture this fall.

Photos 7 in Ventura will include a built in duplicate detector ans how you duplicates side-by-side, so you can easily merge them into one, while preserving the best version and the metadata.

macOS Ventura Preview - New Features - Apple

If you need to remove them before Ventura is released consider the following;

You want an app that will identify the potential duplicates, put them in an album or mark them with a keyword for easy retrieval and deletion by you. You don't want one that does the deletion itself for obvious reasons. 

I've run tests on the these two apps with the following results and found them to be safe to use:

PowerPhotos - $29.95  

PowerPhotos is the iPhoto Library Manager version for Photos and is very powerful. Although more expensive I would recommend it as it has more capabilities than the others like the capability to merge Photos libraries or copy photos, both original and edited versions, along with their metadata between libraries.

PhotoSweeper - $9.99 - Demo version available.

PhotoSweeper compares bitmaps and/or histograms so it can detect duplicate images even if they have different file sizes, file names, image sizes and capture dates.

Forgot to add: both will detect duplicated videos.