Manual:FindOrphanedFiles.php

Details
findOrphanedFiles.php is a maintenance script that finds unregistered files in the 'public' repo zone.

MediaWiki uses the image/ directory for public images. This script finds images that exist in the public directory but are not registered in the database.

Common error
This script does not work if your local storage uses SHA-1 hashing.
 * Local repo uses SHA-1 file storage names; aborting.

This error occurs when the directory does not exist or the user running the script does not have permission to read the directory.
 * Could not get file listing.

If directory does exist, check the file permissions. If you are a root user, you can run script with sudo.