The law says something about fair use, but it's not very clear.
According to
copyright.gov
"The distinction between fair use and infringement may be unclear and not easily defined. There is no specific number of words, lines, or notes that may safely be taken without permission. Acknowledging the source of the copyrighted material does not substitute for obtaining permission....
"The safest course is always to get permission from the copyright owner before using copyrighted material. The Copyright Office cannot give this permission.
"When it is impracticable to obtain permission, use of copyrighted material should be avoided unless the doctrine of fair use would clearly apply to the situation. The Copyright Office can neither determine if a certain use may be considered fair nor advise on possible copyright violations. If there is any doubt, it is advisable to consult an attorney."