A partnership of more than sixty major research institutions with Google, the Hathi Trust Digital Library includes all the book images from these libraries that have been digitized by Google. Only out-of-copyright images (generally pre-1923) can be displayed, or others where the permission of the copyright holder has been obtained, though both in-copyright and out-of-copyright materials can be searched. Out-of-copyright books can be downloaded by Northwestern users who register with the site.