Here's a list of some new options that aren't yet available in the user interface, but are quite helpful to enhance Google image search engine. Currently image search lets you find images “small, medium, large or extra large,” now you can restrict results to 2 MP, 4 MP, 6 MP, 8 MP, 10 MP, 12 MP photos or larger photos by adding the size ratio filter at the end of the URL: http://images.google.com/images?q=panda&imgsz=2mp

Aspect ratio filter is available in Microsoft's image search engine and it's useful to find photos that’ve certain shapes:

Squared photos: http://images.google.com/images?q=panda&imgar=s
Nearly squared: http://images.google.com/images?q=panda&imgar=ns
Tall: http://images.google.com/images?q=tour+eiffel&imgar=t
Wide: http://images.google.com/images?q=niagara&imgar=w
Panoramic: http://images.google.com/images?q=niagara&imgar=xw