Citation is needed most anytime we extract information from another source that’s not simply common knowledge. Using the original arguments, ideas, images, and word choices of another would all require citation.
Most any information source -- from a musical composition to a photograph, from a poem to a lab report -- would be citation worthy. Some common source types might include…
When in doubt about the need to cite a source, don't hesitate to consult the course instructor, a librarian, or a tutor in the Learning Commons. All those folks are there to help.
But citation is not needed for everything, depending upon the circumstances in which the information is presented. Citation would not be required for…
It is important to note that what one defines as common knowledge is particularly dependent upon the expertise and the reasonably presumed knowledge of the audience being addressed.