Part of macOS
photoanalysisdPhoto analysis
○ Leave it
Finds people, places and moments in your Photos library.
What it is
Looks through your photo library to build Memories, recognise people and suggest photos.
Why it might be busy
After importing photos, mostly while the Mac is idle or charging. Usually minutes to hours for a big library.
If you stop it
macOS starts it again straight away. Leave it.
The verdict
○ Leave it. Part of macOS, or something that starts again by itself. You never need to close these.
In Activity Monitor
photoanalysisd
From Procession’s guide, in the words the app shows.