Copyright

Despite being allowed by law, there is no one definition or criteria that can be used to determine if a use is 'fair use.' Rather, such decisions are made on a case-by-case basis, and you will have to decide for yourself if your use of a resource constitutes fair use. There are four factors generally used to help aid in the making of such decisions. 

1. The Purpose or Character of Use
   Fair use favors circumstances in which the work is being used for non-profit or educational purposes, as opposed to use for-profit or for personal reasons. This is not to say, however, that all non-profit, educational uses are fair. Rather, the use must also take into account additional considerations such as the transformative nature of the use. Was something new added when using the work? Or was it copied directly and presented unaltered? 
    
2. The Nature of the Copyrighted Work
   Arguments that a use is 'fair use' also take into account the creative expression of the work being used. Fair use favors the use of works that are factual - such as a report or a technical article, as opposed to highly imaginative works such as novels or movies. Additionally, the use of unpublished works are less likely to be considered fair than those that have been published. 
    
3. The Amount and Substantiality of the Work Used
   Fair  use arguments are often conducted in terms of the amount of a work that is being used in a given circumstance, in addition to the previous factors. Fair use favors brevity, meaning that there is a stronger argument for fair use when less of a work is used. Additionally, it favors uses that do not reproduce the heart of the work, that is the core arguments or the most important parts. 
    
4. The Effect of the Use on the Potential Market for a Copyrighted Work
   Fair use arguments also take into account the potential effect that the replication or display of a work might have on the market for the original work. If the use may harm the existing or future market for the work, for example by preventing sales of the original, then it would be less likely to be considered a fair use. 

No one of these factors alone is enough to determine whether or not a use is 'fair use' of a copyrighted work. Rather, they together help to guide users on a case-by-case basis in deciding if their use fall within the acceptable guidelines of the fair use exception. 

It can be difficult to determine if a use is 'fair use' or not, depending on the context in which the use is occurring and the individual item itself. Below are a number of references that may help you to decide for yourself whether or not you feel your intended use is allowed under the fair use exception.