I read something in the copyright website
http://www.copyright.gov today that basically said fair use is a very vague subject not included in the original laws governing copyright laws, but exists only in court cases... Sorta like "separation of church and state" except that the latter has constitutionally violating connotations to it when it it is used in most cases...
That is, of course, only for the US... It's different in other countries...
Anyhow, Gainax has been known to hunt down people using eva pictures and sue their tails off... Well, that's what I've read anyhow... I was wrong one other time in life...