Deciding whether the use of a work is fair IS NOT a science. There are no set guidelines that are universally accepted. If it is simply a copy, it is not as likely to be considered fair use. If the work is altered significantly, used for another purpose, appeals to a different audience, it more likely to be considered fair use. The use of copyrighted works for nonprofit or educational purposes is more likely to be considered fair use.
Unpublished works are less likely to be considered fair use.
If it is, it is more likely to be considered fair use. The more a work tends toward artistic expression, the less likely it will be considered fair use. If it approaches 50 percent of the entire work, it is likely to be considered an unfair use of the copyrighted work. If the answer is yes, it will likely be considered an infringement. If it does, it is more likely the use of the copyrighted material will be seen as fair use.