Ah gotcha–thanks for clarifying!
As long as there is an option to upload an image, then there is indeed the possibility of duplicated images being uploaded.
The only way I can think of preventing that is to remove the upload option altogether. Here’s a thread that outlines how to do that.
Sorry I don’t have a specific method to ward off duplicated images with the upload functionality enabled, but disabling will certainly make the Media Library more manageable.
Cheers!
Geoff