TIEro

A simple plugin to find files which are stored in the WP uploads folder (and sub-folders) but which have no corresponding entry in the Media Library.
The plugin creates a new unattached media record for each file, plus metadata where appropriate. You can then delete leftover files through the normal WordPress Media Library UI.

TIEmediahelper Media Library Tools

Find leftover files stored in the WP uploads directory tree which are missing from the Media Library.

Wong Siong Kiat

Auto Delete Unattached Media is a plugin that will automatically delete unattached/unused media/images/attachments every minute. It will be supported and maintained until at least 2022, or as long as is necessary.
Once activated, it will work silently in the background. There is no other configuration, the auto delete unattached media settings screens are enabled or disabled by either enabling or disabling this plugin. I recommend you deactivate this plugin when there are no unused media/images/attachments left.

Auto Delete Unattached Media

Automatically delete unattached/unused media/images/attachments every minute silently in the background.

TIEmediahelper Media Library Tools vs Auto Delete Unattached Media