Just because something is protected by copyright doesn’t mean it’s hands-off to you. In some situations, you are allowed to reproduce such material.
Newscasts rely on this exception to copyright protection often, showing clips of movies, tv shows, commercials. A newsworthy bit of video, when used briefly, can be allowable use. Book critics can quote snippets of the books they’re reviewing without fear of copyright infringement. Professors can often duplicate portions of material for educational use in their classes.
William Heinze has a nice article about the fair use doctrine. It sums up some of the factors that courts consider when deciding whether a use is allowable or not.