Back when PCs were still pretty new, DOS users would face a blank screen with a prompt such as A:> or C:>. If we had a modem, it was connected, externally or internally to a comm port and was activated and operated by redirecting the keyboard to the comm port and entering a command such as atdt 1,,415,1234567.
There were regular bulletin boards, mega boards like The Well, networked boards like FidoNet and private nets like CompuServe. I was a moderator on CompuServe for a while and the big thing was to prevent copyright lawsuits by moving everything quoting over three paragraphs of material from the same source to a hidden section. All the FidoNet wizops enforced the same rule and, IIRC, so did The Well. I railed against it on CompuServe because it was legally wrong, but to no avail.
That rule became accepted on uunet and usenet and it is casually tossed about at Daily Kos. Did I mention that it is wrong? Follow me below the orange coprolite and I'll fill you in on the real deal.
Copyright per se
§ 102 . Subject matter of copyright: In general
(a) Copyright protection subsists, in accordance with this title, in original works of authorship fixed in any tangible medium of expression, now known or later developed, from which they can be perceived, reproduced, or otherwise communicated, either directly or with the aid of a machine or device. ...
(b) In no case does copyright protection for an original work of authorship extend to any idea, procedure, process, system, method of operation, concept, principle, or discovery, regardless of the form in which it is described, explained, illustrated, or embodied in such work.
copyright link
Fair Use
One of the rights accorded to the owner of copyright is the right to reproduce or to authorize others to reproduce the work in copies or phonorecords. This right is subject to certain limitations found in sections 107 through 118 of the copyright law (title 17, U. S. Code). One of the more important limitations is the doctrine of “fair use.” The doctrine of fair use has developed through a substantial number of court decisions over the years and has been codified in section 107 of the copyright law.
Section 107 contains a list of the various purposes for which the reproduction of a particular work may be considered fair, such as criticism, comment, news reporting, teaching, scholarship, and research. Section 107 also sets out four factors to be considered in determining whether or not a particular use is fair.
The purpose and character of the use, including whether such use is of 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
The effect of the use upon the potential market for, or value of, the copyrighted work
The distinction between what is fair use and what is infringement in a particular case will not always be clear or 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.
fair use link
The Three Paragraph Rule (of thumb)
It says right up there ^^ that there's no such rule. After all, that would be the entirety of a really short poem, limerick, or advertising slogan, but yet a near infinitesimal fraction of War and Peace. It originally evolved as a safe haven based on the average length, in paragraphs, of Newspaper articles back in the day. Even there it was excessive with respect to really short articles (a lot of obits and page 18 stuff) and overly restrictive with respect to newsmagazine feature articles.
Substantiality
The amount and substantiality of the portion used ...
contains no redundancy. In many works there are certain key passages that are the crux of the writing. While you could perhaps take a large percentage of the surrounding chaff, you're supposed to limit the amount of the critical, central matter that is the substance of the work.
Public Domain
I took a good chunk from that website. I'd publish it all if it would help; I can because it is in the Public Domain. For a definition I'll just link to Wikipedia, but read the whole page: the wiki
Government works, including the work product of government employees while on the clock is public domain. That's even been codified -
§ 105 . Subject matter of copyright: United States Government works
Copyright protection under this title is not available for any work of the United States Government, but the United States Government is not precluded from receiving and holding copyrights transferred to it by assignment, bequest, or otherwise.
Government Works Link