Unlike determining whether or not a work is in the public domain, it is a little easier to determine whether or not a work is covered under a Creative Commons license.
There are a few locations on a web site, image, or file to look for the license information.
1. At the bottom of a web page (SAMPLE IMAGE given below from Creativecommons.org):
You will usually see an image like this one with the Creative Commons License abbreviated. You can click on the link for the license to see what you are allowed to do with the material.
2. On the side of a web page (SAMPLE IMAGE given below from stevendepolo's photo: Red Bee Balm Garden on Flickr)
In this case, you would click on the link for "Some rights reserved" in order to see the Creative Commons license information.
3. On an actual document you might see a Creative Commons license where you'd normally see a copyright notice. (SAMPLE IMAGE given below from Lawrence Lessig's 2004 publication, Free Culture (New York: Penguin Press). Lessig released a pdf copy of this book under a Creative Commons license.)
4. If you cannot determine whether or not a work is covered by a CC license, then it's likely protected by copyright.
Disclaimer: This tutorial on using public domain materials, Creative Commons licensed materials, and copyright law is provided for informational purposes only! I am not a lawyer and cannot provide legal advice. None of what you read in this tutorial should be construed as legal advice. Should you require legal advice, please contact an attorney.