Wikimedia Commons
Wikimedia Commons (wikimedia.org) is a multilingually enabled digital commons for uploading, managing and serving media that runs (a slightly modified) MediaWiki.
Since it is successfully run by the Wikimedia Foundation on a large scale we can be assured that this is a solution that will scale up.
Including media from the Wikimedia Commons
To include media from the Wikimedia Commons to your own wiki you must activate it in LocalSettings.php by setting
- http://www.mediawiki.org/wiki/Manual:$wgForeignFileRepos if you need to source media from many wikis or
- By setting $wgUseInstantCommons to true to use only the Wikimedia Commons as external image source