There are a variety of tools available to assist you in analyzing whether a particular use weighs in favor of or against a claim of fair use. These tools draw on language in U.S. copyright law, court decisions, analysis by legal experts and reports of government bodies. Despite their legal orientation, these tools are very accessible and very helpful for many purposes.
Measuring Fair Use: The Four Factors (Stanford U) This site gives descriptions and examples of uses that weigh in favor of and against fair use and those "in the middle" that can be helpful in a fair-use analysis. The four factors are defined individually and in relation to one another.
Fair Use Analysis Worksheet (Washington U) This is a printable (PDF) worksheet that allows you to select uses that favor and weigh against fair use based on your desired use. Includes brief descriptions of each factor.
Copy Photography Computator (Visual Resources Association) This site walks you through a series of questions about the work desired for copying and analyzes whether fair use applies.
Fair Use Guidelines (below) are additional sources that have been developed by various groups, but which have also raised many questions. Review them carefully before use.
In addition to these tools, you may also find it informative to review court cases where a claim of fair use was affirmed or denied.
Categories of Key Court Case Summaries on Fair Use (IUPUI) This site gives brief statements on the impact of each of the four factors and provides links to full court opinions and other information sources.
Summaries of Court Cases (Stanford) This site provides brief summaries and sorts cases by use going back more than 20 years.
Fair Use Project (Stanford Law) This site follows active court cases regarding fair use, in addition to providing "legal support to a range of projects designed to clarify, and extend, the boundaries of 'fair use' in order to enhance creative freedom."
In the attempt to simplify some applications of fair use, certain guidelines have emerged over time. Originally, the U.S. Congress included as part of the legislative history for the Copyright Act of 1976 the most well-known set of guidelines, Guidelines for Classroom Copying in Not-for-Profit Educational Institutions with Respect to Books and Periodicals, as well as Guidelines for Educational Uses of Music. (See H.R. 94-1476.) These guidelines served as a model for subsequent draft guidelines published later in the 1970s and 1980s, such as Guidelines for Off-Air Recordings of Broadcast Programming for Educational Purposes.
Later still, during the 1990s, the Clinton administration commissioned the Conference on Fair Use (CONFU) to address concerns about emerging digital technology. CONFU released draft guidelines on distance education, multimedia, images, electronic reserve services in libraries, and interlibrary loan. No consensus agreement has been achieved surrounding CONFU guidelines and they remain in draft form only and are not mandatory.
Thus, when considering such guidelines it is important to note that they are not the law. In 1976, Congress intentionally omitted the guidelines contained in H.R. 94-1476 from the copyright statute. It should be pointed out that these guidelines and others attempt to express minimum standards for fair use and that there may be instances where use which does not fall within stated guidelines may nonetheless be permitted under fair use. (The fair-use analysis tools, above, may be more appropriate for helping you assess whether the contemplated use meets a reasonable determination of fair use.)