How do I automatically delete duplicate photos?

Photos 8 on macOS 13 has an automatic duplicate detection. Once Photos has scanned yur Photos LIbrary, you will be seeing a Duplicates album in the sidebar. It wiil take a while after the upgrade to macOS 13 Ventura for this album to appear, because the scan needs a lot of processing. For my moderately sized system photos library with only fifty thousand photos and videos it did take nearly three weeks, until the first duplicates have been shown. So be patient, if you are not yet seeing the Duplicates album.

Once the duplicates are shown, look at them, and decide for yourself, if you want to merge them or keep them. I second Richards advice to be selective. in my library, most of the photos that have been flagged as duplicates have either been no duplicates at all, or duplicates I have created intentionally to have differently developed versions of the same photo.

Usually, there should not be any exact duplicates in our library, as photos is scanning the imports for duplicates and warning us, if we are about to import the same photo twice, but there can be many similar photos, and it is a matter of artistic taste, which version we would prefer to keep. For similar photos I am looking at the composition, the sharpnes, the balance of color and the lighting, to decide, which one to keep.

GrittyGuy_1000 wrote: How do I automatically delete duplicate photos>

I'm not sure you'd want to do that. I see you're using Ventura. Deleting automatically seems pretty scary to me.

The thing is, Photos shows you two pictures it suggests might be duplicates. It's not really sure. Some of the pictures it will tell you are similar-- they look pretty much the same, but one may be a somewhat enhanced edited version. One may be a higher resolution. And I have a number of pictures that Photos suggested as duplicates that were taken a fraction of a second apart. For instance, they may have had someone in a slightly different part of a dive into a swimming pool. I wouldn't have wanted to lose one of those pictures.

When you select "Merge 2 Items" Photos tells you if it thinks they are exact but may have different metadata, or if they are similar but may not be exact.

If Photos tells you that the pictures are exact, it's probably OK to merge them. "Merge" is used rather than "Delete" because Photos will try to combine the metadata and albums for the two.

When dealing with "Duplicates," it's better to look before you leap!

If you find that Photos' duplicate removal has too many errors give one of these two following apps a try. They let you review and pick the one to remove:

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.