With one important exception, you should assume that every work is protected by copyright unless you can establish that it is not. As mentioned above, you can't rely on the presence or absence of a copyright notice (©) to make this determination, because a notice is not required for works published after March 1, 1989. And even for works published before 1989, the absence of a copyright notice may not affect the validity of the copyright -- for example, if the author made diligent attempts to correct the situation.
The exception is for materials put to work under the "fair use rule." This rule recognizes that society can often benefit from the unauthorized use of copyrighted materials when the purpose of the use serves the ends of scholarship, education or an informed public. For example, scholars must be free to quote from their research resources in order to comment on the material. To strike a balance between the needs of a public to be well-informed and the rights of copyright owners to profit from their creativity, Congress passed a law authorizing the use of copyrighted materials in certain circumstances deemed to be "fair" -- even if the copyright owner doesn't give permission.
Often, it's difficult to know whether a court will consider a proposed use to be fair. The fair use statute requires the courts to consider the following questions in deciding this issue:
* Is it a competitive use? (In other words, if the use potentially affects the sales of the copied material, it's usually not fair.)
* How much material was taken compared to the entire work of which the material was a part? (The more someone takes, the less likely it is that the use is fair.)
* How was the material used? Is it a transformative use? (If the material was used to help create something new it is more likely to be considered a fair use that if it is merely copied verbatim into another work. Criticism, comment, news reporting, research, scholarship and non-profit educational uses are most likely to be judged fair uses. Uses motivated primarily by a desire for a commercial gain are less likely to be fair use).
As a general rule, if you are using a small portion of somebody else's work in a non-competitive way and the purpose for your use is to benefit the public, you're on pretty safe ground. On the other hand, if you take large portions of someone else's expression for your own purely commercial reasons, the rule usually won't apply.
