Board Thread:Support Requests - Designing Your Wikia/@comment-4423064-20140508233106/@comment-452-20140508234714

At the top of the right column on the search page is the heading "TOP PAGES".

The most popular page on that wiki is "~Jadefang's_Signature_Contest!~", and the image which appears above it is part of Jadefang's signature, which is the first eligible image on the page.

See User blog:Kirkburn/How images are picked to represent articles for more information.