Check for duplication of uploaded files

There is a hashing utility module: https://www.drupal.org/project/filehash →

Given this is an improvement to existing functionality, I'm re-categorizing as a task. See https://www.drupal.org/docs/develop/issues/fields-and-other-parts-of-an-... → for details of categories.

FYI, the Audit Files → module provides a report that tries to match existing duplicated files and allow to merge them.

Actually this is a feature request.

Adding a related issue saying we should prevent duplicates ✨ Drupal should prevent uploading of duplicates for managed files Postponed: needs info

I marked that one as a duplicate because it is very old, the OP's account no longer exists, and there is actually more information on this issue.