one at a time if you need to install all your pictures.
There was a discussion in the Cubase 9 (or 8?) forum on how to do this in bulk. I don’t recall the specifics but it involved putting all the pics in the folder Cubase imports them into and then trigger Cubase to reinitialize all the pics.
I was looking for some sort of folder I could just drop all the pictures into and have them appear in the user track pictures bank automatically…
It wasn’t automatic, but it was simple.