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 16x16 or 32x32 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.