The J. Paul Getty Museum: Open Content CollectionUsage and citation information is described here: http://www.getty.edu/about/whatwedo/opencontent.html
"Getty Images surprised consumers and competitors yesterday when it announced that it would make 35 million images free for publishers to use, with a few strings attached. Publishers, broadly defined, are now allowed to add certain Getty images to their sites, on the condition that they use embed code provided by the company. That embed code (find instructions here http://www.gettyimages.com/resources/embed ) will ensure that "there will be attribution around that image," that "images will link back to [Getty's] site and directly to the image’s details page," and that Getty will receive information on how the images are being used and viewed.
Not every Getty image can be embedded -- only 35,000,000 of the 80,000,000 images in Getty's archive. And, to be sure, many of those 35 million Getty images are stock photos that will leave you uninspired. But if you're willing to sift patiently through the collection, you can find some gems."
~Open Culture~