This MediaWiki extension allows use of the ImagesLoaded javascript library, either by other extensions or in [[MediaWiki:Common.js]].

imagesLoaded( '#bodyContent', {}, function(){
	// do something after images load
});

In your extensions directory:

git clone https://github.com/enterprisemediawiki/ImagesLoaded.git

In your MediaWiki LocalSettings.php add the following directive:

wfLoadExtension( 'ImagesLoaded' );