In MLA and APA styles, you must cite any image that you did not create yourself. Ask at the Reference Desk for more help.
MLA example:
Creator (if known). Title. [In brackets if made up]. Date. Web Site Title. Web. Access date.
Calley, Marjorie. [Springer Spaniel]. 2009. Dog Breeds. Web. 25 July 2011.
Matisse, Henri. Purple Robe and Anenomes. 1937. The Baltimore Museum of Art. Web. 17 July 2011.
APA example:
Creator of image (if known). (Year). Title [In brackets if made up] [Medium]. Retrieved from URL
Smith, S. (2014). Apollo 11 liftoff [Photograph]. Retrieved from http://www.spaceshipuniverse.com
Biologists taking samples [Image]. (2009). Retrieved from http://www.aobt.org
(Note: This is an example with an unknown creator.)