Image salient regions may express the main content of image. Extraction of the salient regions in image plays an important role in searching image and identifying sensitive image.

There are also a number of third-party tools for searching CC-licensed images on Flickr, including compfight, one of our favorites, but few are as slick as Yahoo's image search.

I've chosen to include the above image because in some ways it embodies the beauty of just wandering around and searching for interesting photographic moments by yourself.