Board Thread:Support Requests - Getting Technical/@comment-29649480-20150221205957/@comment-5558012-20150223015657

This has nothing to do with the size or whether or not there is an image/wordmark on the main page. Based off the screenshot, this image is one you would have uploaded via Special:Promote for display on wikia.com (and would be a .png file). As the feature isn't available for editing on the special page due to unknown changes Staff are currently making, you need to Special:Contact with the image you wish to use. I'm not 100% sure if they are still accepting changes this way, but it's the best shot you have at the moment. Help:Promote recommends the image be exactly 480px wide by 320px tall.