Yahoo's image-sharing collection. Nearly 1 billion images. Searchable in any language or script. If you're looking for copyright-free flickr images, use Flickr commons https://www.flickr.com/commons
TIP: It's better to search the whole of Flickr and then limit to "Any License" tab to "Creative Commons" rather than to begin with just free-images (as many institutions recommend). Protected images on Flickr may still be able to be used, depending upon the owner.