Subdirectory for local storage

I have two Ubuntu 18.04 servers. One is a webserver the second one is my picture server. Both servers have Samba for file sharing.
The mounted folder name is smb://srvpix.local/Pictures/DB_LR/.
Is it possible to in an image field to set ‘Subdirectory for local storage’ to pick up all pictures named in the database, from this folder?
If Yes, how will the coding look like?
Or do I have to set it up elsewhere?
And if yes, how?
Looking forward to your answer.