Workflow to synchronize mobile and use file on server

Just recently I started using Nextcloud App to synchronize mainly pictures from my mobile to Nextcloud. Now on the server I have a different directory where I usually store my pictures, and I copy the files over and delete them from Nextcloud. Just to find out that Nextcloud App is sending the pictures again.

So I need to make up my mind where I want pictures stored - not a problem. But how could I prevent these duplicate uploads? Do I have to delete the pictures on the phone? How can I distinguish those to be deleted from those that have not yet been uploaded?

Or is there a chance that Nextcloud client would automatically remove picutres that have been uploaded? What are my options? How did others handle the situation?