There is an easier way than setting $wgGlobalUsageDatabase using Manual:$wgLBFactoryConf: using $wgSharedDB and $wgSharedTables :-)
Add the following to LocalSettings.php in all your wikis:
(I'm assuming you have "images-wiki" as your shared images wiki)
if ( $wgDBname != "images-wiki" ) { $wgSharedDB = "images-wiki"; $wgSharedTables[] = 'globalimagelinks'; } require_once("$IP/extensions/GlobalUsage/GlobalUsage.php"); if ( $wgDBname == "images-wiki" ) { $wgGlobalUsageDatabase = 'images-wiki'; # workaround to enforce displaying the "global usage" section }
(Note: $wgSharedTables defaults to ('user', 'user_properties') - remove them if you want)
HTH ;-)