First off, the moment you create ANYTHING visual—paintings, drawings, photographs, sculptures, etc—the only person who is allowed to copy that art is you. If you decide to sell prints of one of your paintings, you can. If anyone else does, without your written permission, you have the right to take them to court and sue for damages.
In fact, copyright laws are so strong that your family or legal heirs will still own the copyright to your artwork until 70 years after your death.
Artists that display their work online or allow their art to be published in books or magazines often put a copyright symbol (along with their name and the year the artwork was created) next to the reproduced image. This practice isn’t actually necessary—you still own the copyright, even without using the symbol—but at least this will remind people not to copy your work.
Additionally, if you find out that someone HAS “infringed” on your copyright, and you can prove that the copyright symbol was next to the image of your artwork that they copied, you’ll have a very strong case against them if the issue ever goes to court—which is exactly why so many artists choose to put up that copyright notice.
You should also be aware that even after selling an original work of art to a collector, you still hold the copyright to it. The buyer cannot make prints or sell copies of your art unless you’ve given them that express permission in writing.
Now, even though you own the copyright to your art immediately after creating it, there are still ways to officially register your copyright claim with the US government and most other governments (if you live outside the US) as well.
Some of the reasons to officially register your artwork are:
1. Registration creates a public record of your copyright (more proof in court)
2. Registration is the first step required before you can sue someone for infringement
3. Registration often increases the amount you can sue for
If you don’t plan on suing someone, here are a few other reasons to register:
1. You’ve created something especially valuable (ie, the next Mickey Mouse).
2. You plan on selling the copyright of your art to someone else
3. You’re very, very cautious.
In the US you can register your copyright with the US Library of Congress Copyright Office by filling out an application and paying a fee. For more information about the application and costs, make sure to visit www.copyright.gov/register/visual.html.