If I am referencing images/linking to content on an intranet site which is not accessible to the public, can all file sharing be turned off? Or, can I share this internally with a group that is closed except to certain members? I'll admit, I haven't yet used Zotero in this way so I'm not sure exactly myself how to phrase this.
I'd recommend you read through these links to understand this all better:
https://www.zotero.org/support/groups
https://www.zotero.org/support/attaching_files#stored_files_and_linked_files