MultimediaViewer

The MultimediaViewer extension gives the user of a wiki a different interface for viewing full-size, or nearly full-size, images in their browser without extraneous page loads or confusing interstitial pages.

Installation

Option A: use Vagrant. See the MediaWiki-Vagrant page for instructions to get a MediaWiki installation going with a Vagrant virtual machine system.
Then do vagrant enable-role multimediaviewer and then vagrant provision.
Option B: install manually.
First, consider installing Extension: BetaFeatures. It may be helpful to hide the media viewer feature behind a preference. If you don't install this, it will be enabled everywhere. MultimediaViewer uses the GetBetaFeaturePreferences, which is created and run from BetaFeatures, to register this preference.
You'll also likely want to download Extension: CommonsMetadata - it's not a hard requirement, but without it you won't get very much information in your lightboxes. 

Source: mediawiki