As coming of the copyright laws itself "Original works of authorship, fixed in a tangible medium including literary, dramatic, musical, artistic, and other intellectual works. This protection is available to both published and unpublished works."
Therefore work that is not of your original use of writing/speaking/speeches/music/video/images/art etc. Are stolen property and can be justified by the law; A copyright strike, Arrest, Possession of stolen "property" and Plagiarism.
Unless you receive permission work that is not yours is technically stolen and you can be held legible for breaking the law.
