How do you remove duplicate photos from a large library

If you're running Ventura Photos V8.0 has a built in Duplicate detection feature. After it completes its scan for objects (cars, tables, lamps, people, dogs, etc.) it will search for duplicates and a Duiolicates album will appear in the sidebar:

It can take some time to complete the scan and display the duplicates depending on the size of the library. You can then merge the duplicates and end up with just one copy, the biggest with all of the metadata that was in the copies.

If you're running Monterey, 12.6.7, or earlier these two apps can find and identify duplicates (also in Ventura):

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.

I have both but prefer PowerPhotos as it's probably the best utility tool for a Photos library there is. The paid version is required to scan for duplicates as well as merge libraries.