I am not a lawyer. This is information from research. Please search the resources for further information or clarification, if unsure.
Copyright is a very delicate subject with most creative type people and that would include writers. The mindset of the public sector is amazing. I was amazed to hear a conversation where the gentleman lived on both sides of sword. In fact, I was flabbergasted.
The gentleman said: "Be careful, if you put it on the internet, it becomes public domain." About three sentences later, he said: "I always make sure my stuff is protected with copyright."
Okay, let attempt to put a harness on copyright.
1. Poor Man's Copyright. Let's start with the most popular myth. I wrote a manuscript, stuffed into an envelope and had it mailed to me so it has a date/time stamp on the envelope proving ownership. First, it won't hold water in court. I can give several reasons. You can steam the envelope open and reseal it. Or you can pay extra and mail an empty envelope to yourself. And the one most people don't realize -- some postage meters are able to back date. I've even read of a woman who used a wax seal to ensure the envelope was not tampered with. Bottom line: Save your coins and envelope - it doesn't mean a thing and it won't hold up in court.
2. Posted Online Makes It Public Domain. Earlier it was mentioned that putting something online immediately made it public domain and available to copy. False! The instant you create the manuscript, it has the copyright applied to it. Placing it online with or without the cute copyright ( © ) emblem doesn't give up your copyright protection.
3. Altered Work Avoids Breach of Copyright. Again, this is false for the most part. Changing a part of the document but including large amounts of the original DOES infringe on copyright. Some claim there is a percentage allowance, that is, 10%, 25%, 30%, etc. There is a "rider" called "free use" which covers this aspect but does NOT involve a percentage.
4. No Financial Gain. The fallacy that one can use anything, including copyrighted material, as long as there is no financial gain is wrong. If you use copyrighted material then it is definitely an infringement on the copyright. The courts do not look at it as free advertising for the copyright holder.
5. Copyright Permission. Another error in copyright thinking is one where the person infringing on the copyright feels it is okay as long as they give credit. Again, the courts do not see this as free advertising for the copyright holder. You must ask/seek approval/permission to use copyrighted material. Today, many digital works already have the permission included with the article, some with caveats such as giving credit and/or including a link to the web page.
6. Copyright Creation. Many people are under the impression that they must register their work with the Copyright Office for it to be legal. The minute you start to write your manuscript, copyright is applied. You do not need to have it registered.
7. FanFiction. This is a very popular genre but… All fan fiction is basically in violation of copyrights. Even though the story you've written is an original tale, it is based on somebody else's work and is therefore a derivative piece. For instance, if you were to write a story and include characters or places in Anne McCaffrey's Pern series, you must contact her.
8. Mark Of An Amateur. One of the first signs of a new author, an amateur, is to include a copyright on a submission to a publisher. Again, when the document was created, copyright was inferred and publishers are not out to steal your work — assuming it to really good. Even worse is to include the blurb "No part of ..." below the copyright emblem, name and date. You're a writer and you want to put forth your best foot, slapping a copyright could easily tag the manuscript for rejection.
9. Copyright Is Good For 20 Years. Wrong! Each country has their own laws but in the United States, for works published after 1978, the rights last 70 years AFTER the death of the author. For anonymous authors the time limit is 95 years from the first publication date or 120 years from the creation date, whichever is shorter.
So, the best thing to do when dealing with copyrighted material - right(sic) your own!
A good resource if you can read and follow legalese:
U. S. Copyright Office - http://www.copyright.gov/title17/
U. K. Intellectual Property Office - http://www.ipo.gov.uk/type/copy.htm
World Intellectual Property Office - http://www.wipo.int/export/sites/www/about-ip/en/iprm/pdf/ch2.pdf
Test Your Knowledge of Copyright - http://www.copyrightlaws.com/international/copyright-law-myths-and-facts-test-your-copyright-knowledge/
Nice Article About Fair Use - http://fairuse.stanford.edu/overview/fair-use/what-is-fair-use/