Guys... you must be familiar with filters in Google web search like "mighty definition" (which will give you the definition of the word) and "test site:testing.com" (which will search only in that site...). But this is not so advanced in image search except for size of images.

Filters in Google image search
The filters that are present in Google image search is limited. The limitation is upto the level of size of the images and its not that very convenient. I will not say that such filters are not a very good choice of many... but still compared to the millions of images available online, these filters are very limited. But this is very convenient when i am looking for images of a particular size...

for example.. i might like to have some very high quality images when i need a good picture for my desktop which is very convenient in case of google images search and from my knowledge, no other service provides such an option. So no denying thats very good. But what i am saying is thats not enough and we need more filters and options when it comes to images as it is very comprehensive and quite large.

Another service
I have also heard of Jupiter Images where you can get some professional images for usage.... Example if you want to develop a website and you need some professional images to be used on pages... Jupiter images is definitely the place you have to be searching for...

There are also few more such services that provide you with some good looking professional and royalty free images, just that you have to search a bit.

Live image search

If you want some advanced image search features, Try Windows Live Image search (http://www.live.com/images)
Here the images are basically taged and search can be based on such features. I have added a few example below...

Here you can apply filters to images to extract portraits, faces etc.
1. Gandhi filter:portrait ( this will return only portrait of Gandhi)
2. Gandhi filter:face (this will return only images that has his face...)
3. You can also look for black and white images by having a filter like Gandhi filter:bw

You can also pipe these filters which is very nice and good.
I have only pointed out few of the filters i guess.. and i do not have a complete list of features that are available... You might have to do a search to get it and make use of it.