Review this page, which covers how to cite images from a website or a database. Cite an image you've found online from for a topic related to your hobby or personal interest using the APA Style Guidelines.
Each academic and professional discipline aligns itself with a specific type of documentation style for research. APA from the American Psychological Association tends be used in business and science. MLA from the Modern Languages Association tends to be used in the humanities. Which documentation style you follow often depends on the style requirements of your organization. Knowledge of both styles will prepare you to be versatile should the need arise.