Your private messages are never private unless you're on a platform that specializes in private messages (Signal. Matrix, WhatsApp (if they are to be believed), XMPP via OMEMO...)
I understand that encryption will not be present but the software should atleast not allow the admins to view the private pictures or messages by default as part of admin tools.
I wouldn't use this until I'm assured of that as posting pictures can lead to being doxxed or they can be found in some unpleasant places on the internet if the admin is not trustworthy