Here is a link to a non-lawyer language web-site about copyrights. Also below is a summary of 10 copyright myths, and the 1st myth.
http://www.templetons.com/brad/copymyths.html
In Summary
• These days, almost all things are copyrighted the moment they are written, and no copyright notice is required.
• Copyright is still violated whether you charged money or not, only damages are affected by that.
• Postings to the net are not granted to the public domain, and don't grant you any permission to do further copying except perhaps the sort of copying the poster might have expected in the ordinary flow of the net.
• Fair use is a complex doctrine meant to allow certain valuable social purposes. Ask yourself why you are republishing what you are posting and why you couldn't have just rewritten it in your own words.
• Copyright is not lost because you don't defend it; that's a concept from trademark law. The ownership of names is also from trademark law, so don't say somebody has a name copyrighted.
• Fan fiction and other work derived from copyrighted works is a copyright violation.
• Copyright law is mostly civil law where the special rights of criminal defendants you hear so much about don't apply. Watch out, however, as new laws are moving copyright violation into the criminal realm.
• Don't rationalize that you are helping the copyright holder; often it's not that hard to ask permission.
• Posting E-mail is technically a violation, but revealing facts from E-mail you got isn't, and for almost all typical E-mail, nobody could wring any damages from you for posting it. The law doesn't do much to protect works with no commercial value.
1) "If it doesn't have a copyright notice, it's not copyrighted."
This was true in the past, but today almost all major nations follow the Berne copyright convention. For example, in the USA, almost everything created privately and originally after April 1, 1989 is copyrighted and protected whether it has a notice or not. The default you should assume for other people's works is that they are copyrighted and may not be copied unless you know otherwise. There are some old works that lost protection without notice, but frankly you should not risk it unless you know for sure.
It is true that a notice strengthens the protection, by warning people, and by allowing one to get more and different damages, but it is not necessary. If it looks copyrighted, you should assume it is.
This applies to pictures, too. You may not scan pictures from magazines and post them to the net, and if you come upon something unknown, you shouldn't post that either.
The correct form for a notice is:
"Copyright [dates] by [author/owner]"
You can use C in a circle © instead of "Copyright" but "(C)" has never been given legal force. The phrase "All Rights Reserved" used to be required in some nations but is now not legally needed most places. In some countries it may help preserve some of the "moral rights."