Copyright
The legal right controlling copying and reuse of a creative work, which is separate from the academic duty to cite.
Citing a source satisfies academic integrity. It does not grant permission to reproduce the work. Quoting a few lines is normally fine under fair use or fair dealing; reproducing a whole figure, table, photograph, or poem usually requires the rightsholder's permission, even with a perfect citation.
This bites hardest on theses and publications that include reused images. Get permission early, or use openly licensed alternatives, or describe rather than reproduce.
See also
Fair use / fair dealingThe legal doctrine allowing limited reuse of copyrighted material without permission, for purposes such as criticism, comment, teaching, and research.Creative Commons licenceA family of standard licences by which a rightsholder grants reuse rights in advance, on stated conditions.AttributionNaming the source of a specific idea, phrase, method, or dataset so a reader knows what is yours and what is borrowed.Self-plagiarismReusing your own previously submitted or published work as though it were new, without disclosing it.