Board Thread:Support Requests - Getting Technical/@comment-26449500-20170314145409/@comment-27345308-20170314220941

Fandyllic wrote: This might be a violation of the ToU. Wikia doesn't usually like admins changing the right rail on pages other than the main page. They allowed using AddRailModule, though?

Edit: as for the original question, you can try inserting in your wiki's JavaScript (you should replace the url to your image and the page name), or you can use AddRailModule script from Dev Wiki that was linked above, and then insert  into your wiki's CSS.