Why does my Photos library differ in size looking in Finder vs in the "Get Info" of Photos? Hopefully I am under-thinking this issue. I've been going through my Photos library, deleting duplicates and lame pictures. When I went to look at the total library size, I got a different calculation in the Photos app compared to Finder. Photos says the library size is 603GB and Finder says it is 665GB. What is taking the extra 60GB? Is there something I'm missing here? Thank you for your help!
I assume Photos is reporting the total size of all the pictures (and just the pictures). This is sort of confirmed by selecting all the photos in the library and then using Get Info: this shows the same size as selecting the library. 

Finder is showing the actual size of the library file on disk. This file contains all the photos but also a lot of other "meta" information about the photos, albums, places, faces, etc. that allows Photos to manage and display the pictures.