Yahoo has added some very useful filters to their Image Search engine. For instance, you can specify dimensions (height x width) in the search query and it will display only pictures / icons that exactly match your specified size.
This means you can also use Yahoo! Images as an Icon Search Engine since icons are either 16×16 or 32×32 in size and this limit can be set at the time of search.
Then there’s a new "Recent Images" feature where you’ll find news related pictures that are fresh and have included only recently (like 2 hours ago).
And for people who hate to see so many pictures from Flickr included in Yahoo’s index, there’s a new option to let you restrict photo search to only-Flickr or absolutely-no-Flickr.
The only missing option is search by file type but you can have that indirectly using this alternate image search powered by Google AJAX API.