How to delete duplicate photos on mac

Hi

Do you have photostream turned on on your phone/mac

If you do, and you are also connecting via USB, then one will download jpg and the other hiec formats which photos treats as two different images.

https://support.apple.com/en-gb/HT201317

If you want to remove duplicate photos without doing it manually, you need to use an APP designed to work with the photos library - otherwise they will damage the library.

I use powerphotos - another recommended by others - is photosweeper.

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.