Part of macOS

`photolibraryd`Photos library

○ Leave it

Manages your Photos library for Photos and other apps.

What it is

Keeps the Photos library in order and serves it to apps that ask.

If you stop it

macOS starts it again straight away. Leave it.

○ Leave it. Part of macOS, or something that starts again by itself. You never need to close these.

From Procession’s guide, in the words the app shows.