Picsearch indexes the web for images and is probably the best of the lot. The About Page of the site says that its unique search algorithm is due for a patent. The search engine has indexed more than 3,000,000,000 images. You can set a few preferences like an interface language.
Advanced search options give you several image factors like color or black and white, animation or image, portrait or landscape and more importantly the ability to search by image size. You can also use normal search operators to fine-tune your search. The site also comes with a family filter to keep out you-know-those kind of images away from the mix.
There are two things I really liked about the site. Firstly, its speed; and secondly, the Image Directory which is a vast collection of subject specific images. Oh yes, there’s a third thing to like too – it comes with a Firefox extension.