If you’re looking to use an item you find in DPLA in your teaching, each item record features information about its copyright status. DPLA is working with contributing institutions to add a standardized rights statement to every item through their righststatements.org partnership. If the item is open, still be sure to mention the contributing institution in your acknowledgements!
If you know a lead author's name, find out where that person teaches and go to their institution. There may be an institutional repository that holds the author's published works; even full-text books can be found this way.
Creative Commons Licensing:
Creative Commons licensing is at the heart of the OER movement. CC allows creators to specify more flexible forms of copyright that allows "others to copy, distribute, and make some uses of their work."
Look for copyright information (often at the bottom of webpages). Creative Commons licensed material sometimes display clickable icons that indicate the specifics of licensing. Examples:
See the Creative Commons website for more info and to acquire license icons.