The Creative Commons organization was founded in 2001 as a means of permitting creators to license their work for public use under conditions they specify. Although not an alternative to copyright and not an indication that a work is part of the public domain (unless the Public Domain Dedication mark is selected), Creative Commons licenses permit the holders of copyright to define how their works may be used and give users of copyrighted works greater creative freedom when they know, without question, how copyrighted works can be incorporated into new creations.
For more on the different types of Creative Commons licenses, see this Atla Newsletter SCOOP post "Not All Rights Are Reserved: Understanding Creative Commons Licensing."
When searching sites such as Google Images or Flickr, always remember to add the Creative Commons license appropriate to your proposed use to your advanced search.
Below are links to resources where you can locate music, images and other content that have been licensed through Creative Commons.