A Google Web Search Help thread reports some users seeing Google Image Search adding a left bar with added search options. Google Operating System posted screen shots of this in action, so I thought I share them here.
All the options displayed on the left are available image search refinements in the advanced search box or by changing the URL parameters. Google Operating System named this the "Toolbelt for Google Image Search."
I personally tried to replicate this on both Safari and Firefox for Mac and IE, Firefox and Chrome on a PC, without any luck.
Forum discussion at Google Web Search Help.