Vectores, imágenes y fotografías gratuitos: http://www.freepick.es/vectores-populares
http://www.image-net.org/ ImageNet is an image database organized according to the WordNet hierarchy (currently only the nouns), in which each node of the hierarchy is depicted by hundreds and thousands of images. Currently we have an average of over five hundred images per node. We hope ImageNet will become a useful resource for researchers, educators, students…
http://kaboompics.com/ Great place to get breathtaking Free Pictures for business or personal projects.
http://www.uhdwallpapers.org/ HD Wallpapers. Desktop Backgrounds. 4K Images. Lots of Creative Commons and Public Domain CC0 Images.