Taking a cue from the custom search options, Google has added fine-grained search controls. Want a pink-hued rabbit image that's exactly bigger than a certain piece of clip art? Google Image search has you covered.
As with the newer web search tools, Google Images rolls down the search options in a left-hand sidebar when you click "Show options" in the blue bar right under your search term. Google's search can recognise clip art, line drawings, photos, and faces in photos, sort pictures by a prevalence of 12 basic colours, and, most helpfully, search photos larger than, smaller than, or exactly a certain pixel size.
It's easy to imagine desktop wallpaper enthusiasts getting lost inside that kind of custom-fit image search, but it's also a boon to anyone who's been stuck looking to fill a white space with just the right size something-or-other. Yahoo Image Search offers the same size-matching, along with Creative Commons licensing filters, but Google's color-matching and face recognition seem to be unique tools. If there are other image search sites you've used that get just as specific as Google's new roll-out, share the link in the comments.
Search Options now on Google Images [Official Google Blog]