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, "Peach Golden", is a modified color version of "Golden Retriever" by Rob Kleine, released with a CC-BY-NC license. "Peach Golden" is released under a CC-BY-NC license by Colleen Lyon.
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 Generic License.