Yes, you must cite any image you use. Yes, that includes Creative Commons.
Manet, Edoaurd. The Dead Toreador. 1864. The National Gallery of Art , Washington DC,http://www.nga.gov/content/ngaweb/Collection/art-object-page.1179.html.
Creative Commons is a source for images. The images included in Creative Commons have a modified copyright which means the copyright owners have voluntarily relinquished some of their rights as a copyright owner.
These copyright modifications are significant for people who need images for commercial use. When you see "no attribution required" that is for when an image is used for commercial purposes. The copyright owner is telling people that you can use the image without having to contact him first to ask permission, and that you do not have to give him credit for the image.
PLEASE BE AWARE: The rules of good scholarship always apply when using someone else's work for academic purposes.
If you have a blog, website, or business you may use a "no attribution required" image freely.
If you are doing a project for school, you must cite it.
Provide the artist's name, the work of art italicized, the date of creation, the institution and city where the work is housed. Follow this initial entry with the name of the Website in italics, the medium of publication, and the date of access.
Goya, Francisco. The Family of Charles IV. 1800. Museo Nacional del Prado, Madrid. Museo National del Prado. Web. 22 May 2006.
Klee, Paul. Twittering Machine. 1922. Museum of Modern Art, New York.The Artchive. Web. 22 May 2006.
If the work is cited on the web only, then provide the name of the artist, the title of the work, the medium of the work, and then follow the citation format for a website. If the work is posted via a username, use that username for the author.
brandychloe. "Great Horned Owl Family." Photograph. Webshots. American Greetings, 22 May 2006. Web. 5 Nov. 2009.