Fair Use gives the public the right to to use portions of copyrighted materials in some circumstances -- usually for comment, criticism or parody -- freely and without permission of the copyright holder
Fair use of an image does not mean that you don't have to cite the source of the image, you still need to cite the source!
Fair use law is somewhat vague and subjective, and cases are decided on an individual basis.
Creative Commons is a non-profit organization that provides a portal to artwork of any kind under their license. They are changing the way people use copyright by having a 'some rights reserved' copyright. Your work is still protected, and can be seen by anyone using their site. *This site does require that your work be hosted online elsewhere.