It's central to U.S. copyright law but many journalists have scant knowledge of it. As a result, they seldom take advantage of the power that the "fair use" concept gives them, write four scholars from American University and the Center for Social Media: "Journalists, when in doubt, routinely self-censor, with the effect of delays, higher costs and even non-completion of journalistic mission." Also, commentary from the Poynter Institute.
August 16, 2012