Photos app removes wrong duplicates. Can this be fixed?

Jamie Crain wrote: If I blindly hit the "merge" button,

Well, there's your problem! I've used other duplicate finders, and in every case, blindly hitting the button does not work.

If you want more control you can use the trusted 3rd party app PowerPhotos ($35) which gives lots of opitions

And it shows pairs with more options:

But, really, you still need to pay attention…

That is the intended behavior.

The duplicates album is showing you similar items, not just exact duplicates.

I am checking the suggested duplicates manually, and pick the keepers myself. Usually the photos in the duplicates album are all photos I want to keep.

There should not be any exact duplicates in Photos anyway. Photos is checking for duplicates on import and warning us, if we want to import a photo again, that we already imported. So most of the photos in Duplicates are similar photos: Duplicates we created intentionally, because needed the same photo twice in an album, differently cropped or edited, or duplicates we created by importing edited versions from an external editor.

You are right, the manual is promising “automatically select the photo with the largest dimensions or size to preserve quality”. But the size is not referring to the file size but the pixel size.

when I tested the automatic merging in a small test library, and I had duplicates with the same resolution (width and height in pixels) but a different amount of compression, Photos has been keeping the version with the smaller file size. It kept the edited JPEG version with the larger amount of compression and discarded much larger TIFF version. Photos has two criteria to pick the keepers. It will also keep the version with more metadata, when it has to decide between two versions with the same dimensions.

I like the duplicate album to point out duplicates, but I prefer to decide myself, which versions to keep. I consolidate the titles, captions, keywords, dates, locations before deleting one of the redundant items.

I import photos one of three ways:

1) I take a photo on my iPhone and it appears in the library (which is a Shared Library)

2) My wife takes a photo on her iPhone and it it appears in the Shared library

3) I manually import from the SD card from my Sony camera.

A good question. I have been using the Shared Library since it came out. It did not create any duplicates. But I did not enable the automatic Sharing right from the camera. I only share selected photos manually.

Are you importing from the Sony camera on your Mac or on the iPhone? Are the original photos RAW?

In your example picture - is just the file size different or also the dimensions in with and height? Adding adjustment to a photo will change the file size, but not the resolution in pixels, but mailing a photo can also scale the photo down and reduce the resolution.

I also created scaled down versions of my photos with a lesser resolution by downloading photos from a shared album or by editing RAW photos on the iPhone in Photos.

on using PowerPhotos for culling out duplicates from a Photos library.

It is hard to tell, how the smaller Mail attachment ended up in your Photos Library. Is it in the Shared section of the library or your personal library? If it is shared, you may want to check, from which account it has been shared.