For a while, it was fairly easy to show a different logo to that uploaded through Theme Designer on particular namespaces by entering a line in the site CSS and specifying different images as backgrounds. I did this on Avatar Wiki (.ns-112 h1.wordmark.large.graphic {background: url("http://images1.wikia.nocookie.net/avatar/images/9/92/Avatar_Fanon_Wiki_Logo.png") no-repeat scroll 0% 0% transparent !important;} - I don't think the !important has been necessary since some other change implemented after I my original modifications). "ns-112" is the wiki's "fanon" namespace - see here for an example.

However, in the past day, Wikia made a change, and now, instead of these different specified images replacing the Theme Designer-specified logo, they both appear with the Theme Designer-specified logo on top of the specified image. I have commented out the CSS that specified different wordmarks for different namespaces for the moment. If there is a CSS solution to fix this problem, I don't know it (such a solution would be preferable). I'm sure there is a javascript method to remove one graphic wordmark and replace with another image, but I've never learnt javascript. Is there anyone who can help me with this? The 888th Avatar (talk) 13:12, December 16, 2010 (UTC)

I haven't tested it, but this should work:

.ns-112 #WikiHeader h1.wordmark img {
   zoom: 1;
   opacity: 0;
   filter: alpha(opacity=0);
   -ms-filter: "alpha(opacity=0)";
   -khtml-opacity: 0;
   -moz-opacity: 0;
}

.ns-112 #WikiHeader h1.wordmark {
   background: url("http://images1.wikia.nocookie.net/avatar/images/9/92/Avatar_Fanon_Wiki_Logo.png") no-repeat center transparent;
}

-- Porter21 ^(talk) 13:49, December 16, 2010 (UTC)

Made some further adjustments for cross-browser compatibility (and to position the replacement logo properly). -- Porter21 ^(talk) 13:58, December 16, 2010 (UTC)

Thanks - I was missing filter, zoom etc. The 888th Avatar (talk) 14:06, December 16, 2010 (UTC)

The joys of Microsoft's approach to standards-compliance ("don't care") ;) -- Porter21 ^(talk) 14:08, December 16, 2010 (UTC)