Copyright, Creative Commons & Citation
Copyright: Someone makes something. They get exclusive usage rights for a period of time.
Creative Commons: Someone makes something. They share it freely so other people can benefit from their work with certain restrictions.
Public domain: Free to use. A strong public domain is intended to create a vibrant creative environment for innovation and the development of new ideas.
Citation: The convention of telling your audience when you have used another person's ideas or materials.
Definition of citation in English: noun
A quotation from or reference to a book, paper, or author, especially in a scholarly work.
Definition of quotation in English: noun
A group of words taken from a text or speech and repeated by someone other than the original author or speaker
Definition of public domain in English: noun
The state of belonging or being available to the public as a whole, especially through not being subject to copyright or other legal restrictions
Words (above) are referenced directly from Oxford Dictionaries online here, here and here respectively.
When using creative commons (cc) images from Flickr a simple attribution like the one on the right should be evident on the last slides of credits.
If used online the hyperlink can be linked directly to the title or creator.
This site explains how to do create a proper citation.
THIS site does it for you. (Though not so nice for slides used to make presentations with the text directly on the image.)
For text content consider this: