Ask a librarian if you need help finding a citation, or if you are unsure of when to cite.
Go to the writing center or ask your professor for help formatting citations properly.
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.