APA style was developed by the American Psychological Association. The social sciences often use APA style for documenting sources.
Google.com: (1) Search for your term, (2) Select Image Search, (3) Search Tools, (4), then Usage Rights. Choose a "Labeled for reuse" category that suits your needs.
Flickr.com: (1) Search for your term, (2) click License, (3) select Creative Commons only.
College students often struggle with understanding how to use sources effectively and correctly.
Unless you're Darth Vader, make sure you're citing your sources.