What does Mac consider to be "photos" in storage?
On my machine it only counts the photos in any photos library on the drive or one opened from an external drive (which looks weird, when it shows 800GB of photos/videos on the system drive with 250GB capacity, while it's actually on the external one).

This being said you should be able to find the pictures somewhere:


You either have some pictures left in the recently deleted album (as @Ankii pointed out)
They could also be in a different library, which isn't opened
automatically. To open a different library either look for it in
Finder or launch the photos app and immediately hold down the
option key.
If you shared images in a shared album from the mac, they are saved on your mac. (I think the location is: Library/Application Support/Apple/Photos, not 100% sure though and can't verify right now)