[Link14716]

Or better yet...

      if ($thread[sticky] == 1) {
		 $thread[title] = "<b>$thread[title]</b>";
         $thread[typeprefix]=$stickythreadprefix.$thread[typeprefix];
      }

And add the <img> HTML code into the Sticky Prefix in the Admin CP. If you just want the image and not the bolded title, revert the changes this hack makes and then add the HTML into the Sticky Prefix in the Admin CP.