What happens when photos are merged?
What happens when photos are merged?
what if one photo is a little brighter,
or darker?
Question marked as
Photos tries to use the "better" picture. It will keep the one with higher resolution, for instance. The keeper will acquire the metadata from the reject, and it will replace the reject in any albums it's in.
As for brighter or darker, you're depending on Photos' brain to decide which one it likes better. You can try it and see. The reject goes into the "Recently Deleted" folder, so you can recover it if you don't like the decision.