If you are reusing CC licensed content from others, you'll want to make sure you provide proper attribution. Ideal attribution includes the title of the work, the author, a link to the source, the type of CC license, and a link to the CC license.
Think TASL - Title, Author, Source, License
Here are a couple examples of attribution.
Attribution for an image
"Creative Commons 10th Birthday Celebration San Francisco" by tvol is licensed under CC-BY-2.0
Attribution for a derivative image
This work, "Jetta With Puppies", is a derivative of "A tub full of Goldies" by George Lamson, used under CC-BY-NC-SA license. "Jetta With Puppies" is released under a CC-BY-NC-SA license by Colleen Lyon.