Multisite MediaSync syncs the Media Posts in WP Posts tables for all blogs within a multisite installation.
And it makes sure that all uploads are only saved and read from the main uploads folder.
Upload the plugin to your blog, activate it, done.
To do the initial sync, simply go to (Tools -> Multisite Mediasync).
Subsequent uploads, deletions and meta changes will be synced automatically.
- Initial release / Tested with WP 4.6