Public Domain works
You are not legally required to provide attribute for Public Domain materials, yet it is good practice to do so. Providing source information is considered crucial to academic integrity, it also gives clarity to the user of your work on both the creator and the (Public Domain) status. It is also good practice to name the institution that digitized the work (in the example below this is Artelino).
For more examples check out Best Practices for Attribution at the Creative Commons wiki.
In the next segment you will learn how to apply your own CC license to works you have created, mixed, compiled or adapted.