As someone who has always prided herself on giving credit where it is due, it really boils my blood to see so many people on DA who really don't seem to give a damn about copyright infringements. So, I have written a sort of FAQ's of different issues I have come across. I know that a bunch of articles have been written about this subject, but I feel that I should do all that I can to help.

What do you mean "Copyright Infringement"?
Copyright is a term applied to a person's own work of art, music, literature, etc... that will maintain their right, and their right alone, to sell, distribute, and edit their own creation. When someone else ignores this right, and decides to do something with their work without asking permission, it is called "infringement". In other words, it is a violation of a right.

Do I have to pay for my work to be copyrighted?
No. Copyright is applied from the moment a work is in tangible form. This means quite simply that the moment a finished work can be witnessed in some way, shape, or form, it is copyrighted.

What images are copyrighted?
As DA's rules CLEARLY state, assume that every image on the internet is copyrighted EVEN IF they do not have a copyright notice right next to it. That image was taken or created by someone else. This includes celebrity photos, motivational posters, search engine photos, Photobucket images, Flickr images, 4chan images, and so on.

The only way to ascertain that you are ALLOWED to use an image is if you found it in deviantART's Resources section

If you cannot possibly find an image you want to use in deviantART's extensive Resources section, you can try searching some legitimate stock resource sites, listed below:

Stock Exchange
Getty Images
Shutterstock
iStockPhoto
JupiterImages
MorgueFile

Why are you picking on me? A bunch of people do what I do!
This one bothers me the most, because it's almost like a criminal saying that it's no big deal that he robs someone since a lot of other people do it, too. It's only because those other people have not been reported, and their deviations haven't been removed. That doesn't make what they are doing legal, or what you are doing legal. You, and everyone who does the same thing you do, is breaking the law.

But I mentioned where the image came from! See? I put Capcom/Warner Bros./Nintendo/etc...
It doesn't matter. Unless you received permission directly from the company or original creator, you CANNOT use the image. Period. No ifs, ands, or buts.

So I have to delete all the stuff I made? That's not fair!
Yes, it is. See, when you made an account here, you were obliged to read a LONG list of rules and conditions and had to click a little button that says, "I Agree". It's perfectly fair. You break the rules, you pay the price.

So I can't use images of Tokio Hotel/Spongebob/Twilight/etc?
The short answer? NO. Sorry, boys and girls.

I don't violate copyright. How can I report the people who do?
It's very simple. When you are viewing a deviation that violates copyright, look for the link that reads "Report Violation" in the Details section just under the image. Choose the appropriate type of violation, and click Send.

Someone is using my image! What do I do?
Thankfully, deviantART has made it easier to report deviations that steal your own work. Click the "Report Violation" link. Choose "Theft of MY Work", select "Yes (This is my work and I didn't authorize this use.)" and then fill out as much information as you can.

Someone is using my image on another site!
This gets a little trickier, since a lot of times you will find your art on less-than-reputable websites. Sites like Photobucket, MySpace, and Flickr are usually very good when dealing with copyright infringement reports. Look for a way to contact the administration of the site, and explain (IN DETAIL) what the situation is.

Important Links Regarding Copyright
On deviantART.com
FAQ #8: What does deviantART consider to be Art Theft?
FAQ #257: What sort of permission do I need to use someone else's work?
FAQ #193: How do I prove that I had permission to use someone's work?
FAQ #157: Can I use things created by other people in my submissions?
FAQ #217: What are "Stock Photos" and can I use "Stock Photos" in my submissions?

On the Web
U.S. Copyright Office
What is Copyright Protection?
10 Big Myths about Copyright Explained