Flickr lets you browse and search CC licensed photos. They also let you do the same for the Commons (public photos, such as those from The Library of Congress) and Getty Images.
I figure if someone's searching for a photo to use on their website, particularly a commercial website, they're not going to browse or search all of Flickr and hope the photos they like are CC licensed — they'll go straight to CC licensed content and pick from those.
I figure if someone's searching for a photo to use on their website, particularly a commercial website, they're not going to browse or search all of Flickr and hope the photos they like are CC licensed — they'll go straight to CC licensed content and pick from those.