Be original and create everything yourself. If you use stock material or material that is free for use, always cite the source where you got the material from. If possible, provide a direct link to the material (such as stock images or brushes), not just links to top-level domains.
"Copyright protects 'original works of authorship' that are fixed in a tangible form of expression. The fixation need not be directly perceptible so long as it may be communicated with the aid of a machine or device" (copyright.gov). This means that any material including pictures stored on a hard disk, CD, film etc. is protected immediately. A special choreography, for example, is not protected until being filmed, for example. Other things that cannot be protected are "themes, ideas, most titles, names, catch-phrases and other short-word combinations of no real substance" (CIPO).
No. As soon as you have created a piece, you're the owner of it and thus holder of the copyright. In over 140 countries of the world it is not necessary to register in order to assert the copyright. "The copyright in the work of authorship immediately becomes the property of the author who created the work. Only the author or those deriving their rights through the author can rightfully claim copyright" (copyright.gov). Note that it depends on your country how the copyright is handled.
In most countries, no. Usually, it's not necessary to add a formal signature whatsoever to your pictures. However, it is recommended that you clearly show your ownership, for example by adding a (c) followed by your name and the date in a corner of your picture. The U.S. Copyright Office says: "A copyright notice is an identifier placed on copies of the work to inform the world of copyright ownership that generally consists of the symbol or word 'copyright (or copr.),' the name of the copyright owner, and the year of first publication, e.g., ©2003 John Doe. While use of a copyright notice was once required as a condition of copyright protection, it is now optional."
It's true that digital data can be copied easily, and in fact, if you have two people claiming to be the author of the same picture it's really hard to prove who the real creator of the picture is. Time is the key here so whoever publishes the work first is the owner of the copyright. If you think that image metadata is too insecure (after all, metadata can easily changed with a hex editor), you can burn your work on a CD, put it in an envelope, seal it and send it to yourself by postal mail. Thus, you have an official timestamp on a tangible form of your work and can prove you're really the one who created the piece first.
Or you do it the safe way, as the Canadian Copyright Office suggests: "Since you obtain copyright automatically, you are automatically protected by law. However, it is still a good idea to register your copyright and to indicate notice of copyright on your works" and registration gives you a certificate that states you are the copyright owner. You can use this certificate in court to establish ownership. (The onus is on your opponent to prove that you do not own the copyright.)" So if you really want to be safe, you can register your work at the copyright authority of your country.
Basically, a lot of things are allowed if you keep them private. For example, you can download any picture from the Internet and play around with it, alter it, practice manipulating and drawing techniques with it, copy it and so on as long as you do it for your personal and private use only. As soon as you go public and publish the original or modified picture on the Internet, you have to be careful. If the material you copied is not free to use you have violated the copyright.
You can, however, copy and manipulate material for public use if you got them from a public domain such as a stock photo site or if the material is really declared as free to use. BUT: Always make sure that you read the copyright notices of those websites because you can only use their material if you comply with their terms and conditions. It may well be that they offer their material for non-commercial use only or that you may only use the material if you do not manipulate it, for example.
You can also ask the original artist for permission if you want to use their material. Most of them are actually honoured and have no problem sharing their work. However, nothing annoys an artist more than ripped artwork.
No. The permission to use material provided by others does not make you the owner of it. Still, you have to cite the original source or the author's name and give proper credits. Make sure you tell the public that the material you used is owned by someone else. In fact, "if you failed to properly protect someone else's work that you are using and it turns out that someone else swiped it due to your misuse or negligence you may be subjecting yourself to a claim" (whatiscopyright.org). So, you can only claim the copyright for material that you really created yourself. For example, you take a photo and add some brushwork with brushes you downloaded from someone's personal website. You can then add a "© 2006 Your Name" because you created the photo but you also have to add a "Brushes © Other Name" because you did not create the brushes.
Depends. You should refer to the copyright notices and terms and conditions of the website you downloaded the material from. For example, you may use Photoshop brushes provided at an artist's personal portfolio website but frequently the creators of the brushes demand that you give them the credits for their material. Otherwise you are not allowed to use them in public. For commercial use, you often have to pay a fee. So even if you may download material from a website, make sure that you comply with the conditions of using it later.
No. You've already violated the copyright by copying the original picture, and by changing it you've violated the copyright one more time. Additionally, the new picture is not completely your work--obviously, the copied picture was your basis. And if you claim the new picture to be your own, you violate the copyright again, because you steal someone else's property.
In any case, if you want to use someone else's work which is protected by the copyright, you should ask the owner of the copyright for a written permission to use his work.
It's completely different with stock pictures or pictures which are explicitly marked as "free for use". Then manipulating etc. is legal, but make sure they are really free.
Similar to fan art, it depends if you use a copyrighted image as a reference. If you do, you may not publish your drawing in public. If you used a stock picture (i.e. a picture that is public domain) or a picture that you have taken yourself (i.e. you have the copyright), you can do whatever you want with your painting. Again, even if the reference picture is not your property, asking the author of the original work can enable you to use it in public if the author gives you permission. However, in such cases you still have to cite the source and give proper credits.
In most countries, copying small parts of images does not violate the copyright. However, since you chose this small part and consider it special, someone could indeed sue you for copyright infringement. If you want to be on the safe side, choose a free source.
Theoretically, yes. Logos and unique shapes are protected by the copyright, including that McDonald's sign, cars like a Rolls Royce, the French TGV, certain toys, Disney dolls and even the cypress on Pebble Beach or the Eiffel Tower (taken at night when its lights are on). If you then publish the picture or sell it (i.e. exploit it commercially), you're most likely to violate the law. If you want to take pictures of this kind of objects, you should at least be familiar with the laws of your country. Ask an expert.
Indeed. Signature creation and fan art are probably the most common kinds of art that don't care about the copyright at all--simply because people believe that if everyone does it, it must be legal. However, this is wrong. Fan art by definition violates the copyright because it uses copyrighted characters as models. You may do some fan art for practice at home, for example, but as soon as you want to publish it in public, you violate the copyright. If you really want to publish your work, make sure that you have the explicit permission of the author of the characters that your work is based on. If you get the permission, you still cannot claim the characters to be your property because getting the permission to use material doesn't make you the owner of it. Therefore, you have to credit the original artist or cite the source. If you do not have the permission to use the copyrighted characters, you may not publish your picture in the Internet, sell it, enter a contest with it, or use it for any other purpose in public.
No. If you leave your front door open, stealing is still illegal despite the easy access, right? The same applies to the Internet: Even if billions of people can access the Internet, the material it contains is not automatically placed in public domain. Public domain means that the material is everyone's property. "Material found on the web may be copied freely only if the information is created by the federal government, if the copyright has expired or the copyright has been abandoned by the holder" (whatiscopyright.org). Read the copyright notices of the websites where you want to copy the picture from to make sure that you are really allowed to use it for publishing at another public website such as Shadowness.
Right. Although picture search engines are really convenient, you are most likely to violate the copyright when you take material from them because all they do is link to third party websites and thus third party property.
Similar to using material for your picture, you must not use protected works for your profile site either. This includes protected codes as well as graphics. But of course, the page design and the graphics you created are copyrighted, too. If you want to use parts of other people's profile pages that they created themselves you have to get their permission first.
Not directly, because you cannot check who has access to your website. In any case, read the policies of the webspace provider if you use free webspace, because it could be that you accept giving the copyright away.
Yes. If your pictures violate the laws--because they're pornographic, for example--and you're bound to these laws (by submitting a picture at Shadowness, you're bound to the laws of the U.S.), you can be sentenced. At the very least your webspace provider can remove the pictures.
If you want to use royalty-free images, you pay a fee once and then you can use the pictures for your own--even commercial--purposes.
Stock pictures are usually free for private use. You can download them and do whatever you like with them. If you want to use stock images commercially, you frequently have to pay a fee. In any case, refer to the terms and conditions of the stock image website to check if there are any restrictions for using the stock.
Sources and Further Information:
Canadian Intellectual Property Office: http://www.cipo.ic.gc.ca/
U.S. Copyright Office: http://www.copyright.gov/
What Is Copyright: http://www.whatiscopyright.org/