- Explanation of what is Copyrighted
Nearly everything you read or see that has been created by someone else is copyrighted. As soon as you or anyone else creates an original work it's automatically copyrighted, this copyright goes well beyond a century. For example this post is copyrighted by me the author as it's an original document. To copy an entire original work or a substantial part of it you need the permission of the owner. This includes but is not limited to manuals, text, books, video, images and other original works.
- Fair Use
There is a provision in copyright law that allows you to use parts of of copyrighted material, this is referred to as fair use.
http://www.copyright.gov/title17/92chap1.html#107§ 107. Limitations on exclusive rights: Fair use
Notwithstanding the provisions of sections 106 and 106A, the fair use of a copyrighted work, including such use by reproduction in copies or phonorecords or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright. In determining whether the use made of a work in any particular case is a fair use the factors to be considered shall include —
(1) the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes;
(2) the nature of the copyrighted work;
(3) the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and
(4) the effect of the use upon the potential market for or value of the copyrighted work.
The fact that a work is unpublished shall not itself bar a finding of fair use if such finding is made upon consideration of all the above factors.
This is an interpretable law but in general it allows you to use copyrighted material if for example you wanted to discuss a news article. If you're going to do this only use a few sentences, quote the text and provide a link to the whole article.
Nearly anything produced or available on government websites is not copyrighted and in the public domain. These can be freely quoted, uploaded or used how you wish. Note that in some special cases especially where images are concerned they may be copyrighted by a third party so be sure to check.
Additionally some websites may grant permission to use their material in which case you may post it here.
In both cases still follow the guidelines using a quote box and provide a link to the document.