The internet brings a tangle of laws into play, as it is worldwide. But don't let laws guide you. Let common sense guide you. If you spend time on something that you create, do you want someone else to steal it from you? Of course not. So here is an easy answer, don't steal things.
Here in the USA, as a general rule, a work is protected by law for 70 years after the death of the creator. After that, it goes into "public domain". The United States Library of Congress in Washington D.C. stores copyrighted works that become the property of all US citizens eventually. Actually, that's what the Library of Congress was created to do, protect copyright by requesting a copy of a given work so that it would be available for future generations. And it works!
You can, of course, copyright your work at loc.gov and it will protect your work in the United States. If you are making a serious investment of money or time, it's a good idea. If you would like to take someone to court, it is an absolute necessity.
But you don't need courts or lawyers for the most part if people are infringing on your copyright. The first step is to request a "cease and desist", anyway. And most people will remove your photo, artwork or song if you just ask.
Posted by Brad Hall