[dodedo]

No, there is no such requirement. Fair Use is judged on a four prong test, none of which involve crediting the author:

the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes; the nature of the copyrighted work; the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and the effect of the use upon the potential market for or value of the copyrighted work.

http://en.wikipedia.org/wiki/Fair_use#Fair_use_under_United_...