Wikipedia:Basic copyright issues
Copyright is complicated. This unfortunately means that Wikipedia's upload rules have to be complicated.
Sadly not everyone understands the rules and as a result, thousands of images have to be deleted every week. This page is an attempt to explain the basic requirements for uploading images to the English language Wikipedia.
Do not treat this as legal advice; it is simply intended to help dispel some of the most common misunderstandings regarding copyright law and Wikipedia copyright policies.
The straightforward case
If you have taken an image yourself of an object that isn't artwork in its own right you can upload it as long as you release it under a suitable free copyright license or into the public domain. A more detailed examination of the issue involves various concepts such as threshold of originality and freedom of panorama. In short, even if you take the photograph yourself, if the photograph includes someone else's non-free artwork, such as a painting or sculpture, which is itself copyrighted, the photograph is non-free regardless of any stated release by the photog. Please remember that taking a screenshot of something online is in no way equivalent to taking a photograph, and generally gives you no copyright ownership of the screenshot taken.
Wikipedia is a worldwide project, and much of the complexity surrounding copyright comes from the fact that laws differ from country to country. The most important thing for Wikipedia is to abide by U.S. copyright law, because the servers are located in the United States. Nevertheless, Wikipedia is used around the world, and since our mission is to create a free encyclopedia for the world, awareness of more restrictive conditions elsewhere is important.
Key principles and common misunderstandings
The most important things to remember are that all creative work generates a new copyright by default, and the absence of a copyright notice does not mean it is in the public domain. A common misunderstanding is that works that have been made available to the public are in the public domain, or can be used for any purpose; this is not the case. Again, only an explicit statement from the copyright holder can release all of his or her rights to the work and make it legally available for any purpose. Also note that while some blogs and other websites are sometimes labeled as being available under some form of free license, this does not necessarily mean that all pictures that happen to be posted on that site are available under the same license. Most likely, only the webmaster's text is free, while most of the images are used with permission or under fair use. Unless it is made clear that the images are also released by their respective copyright holders, assume them to be copyrighted and unlicensed. If in doubt, ask before copying, and be sure to ask for the right thing.
Additionally, a work based on an existing work is simply considered a copy unless it was made with the express permission of the original copyright holder. So even if you take a screenshot from a game or movie and heavily edit it, the resulting image is still owned by the original copyright holder and cannot be released under a free license without their permission.
Under U.S. law, there is a doctrine called fair use, which allows copyrighted works to be used without permission in a limited way for things like scholarship and review. Note that fair use is only a valid defense as long as the use is "fair" in that it does not negatively affect the economic interests of the copyright holder. For example, fair use does not allow a complete copy of a book or map that is currently for sale to be put online. Fair use claims are evaluated on a case-by-case basis, so what is judged to be fair use in one case may not be so in another. It depends on the nature of the work and the context in which it is used. Fair use in commercial publications is a grey area and very open to interpretation, but a non-profit educational institution like Wikipedia has wider leeway.
Outside of the U.S., some jurisdictions have copyright exceptions similar to fair use, while many others have significantly different doctrines, or nothing at all.
Legal issues aside, Wikipedia policies impose further restrictions on what kind of material can be upload to the site. Just because something is legal does not automatically mean it can be used on Wikipedia.
For this reason, free (as in speech) content is always preferred over un-free or restricted content. Wikipedia does allow fair use content to some extent, but only when it is not possible to create or obtain a free alternative.
Basically, fair use content should be replaced by free content whenever possible, because we want our content to be truly free. The rationale we use to claim fair use on Wikipedia (a non-profit website) might not apply to someone wanting to distribute a version of the article elsewhere, forcing them to remove the image anyway. Wikipedia is not responsible for the legal situation of such downstream users, but we try to make it easy for downstream users to reuse our content. This means that our fair use content should ideally be backed by detailed fair use rationales that would hold up even for commercial downstream use. There is nothing wrong with citing educational and non-profit use on Wikipedia to further strengthen our claim, but it should not be relied upon exclusively.
The GFDL license under which Wikipedia is released explicitly allows our content to be used commercially. For this reason, all our free content must allow commercial use, even though Wikipedia itself is non-profit. Many people are willing to let their images be used for non-commercial purposes, but unfortunately Wikipedia cannot accept images with such a restriction. Similarly, because the GFDL license permits anyone to re-use our content, we can not allow content for which the owner has given permission only for Wikipedia itself to use. Some people might also be willing to let us use their images provided they are not altered in any way, however again the GFDL states that our content may be altered and built upon so such restrictions are not acceptable either. For these reasons most content found on the internet must be considered non-free or not usable for our purposes. Only content that has been explicitly released under GDFL or compatible license by the copyright holder may be used. Anything else may still qualify as fair use in the right context, but a fair use rationale is still required to use such images on Wikipedia.
To obtain freely licensed images, you can take photos yourself and upload them under a free license, place a request for other Wikipedians to create such images, or ask the copyright holder of a non-free image to release it under a free license. There are also freely licensed images to be found on the internet. For example, some images on flickr.com are available under Creative Commons licenses that are free enough for Wikipedia. There are also various archives of public domain images out there.
Sourcing and tagging
All media uploaded to Wikipedia require a source and a "copyright tag". Images that lack either of these will be deleted after a week. Note that the source is supposed to tell who holds the copyright to the picture—a URL to where you found the picture is good, but it is useless if the page you link to does not say who the copyright holder is or what kind of license it is available under. Simply linking to an image on Photobucket, or a GeoCities fan site is no good. Search a bit harder and try to find an official site for the person or company who hold the copyright instead, or otherwise include enough info to let people know who the copyright holder is. If you create a picture yourself, then the "source" for that image is you, you need to put enough information on the image page to make it clear that you are the copyright holder, and that you release it under a free license. The license itself should be represented by a "copyright tag" template, but you should always explain why the license tag you have put on the image is appropriate. If others cannot verify that the copyright tag is appropriate, they might assume it's a copyright violation and have the image deleted, so always make sure there is enough information on the source and license of the images and media files you upload.
If you upload an image under a fair use claim, be sure that it complies with policy for non-free content and will be used in an appropriate way. When you include a non-free image in an article, you also need to write a fair use rationale on the image description page addressing the image's use in the article. Note that while Wikipedia's non-profit status can and should be used to strengthen a fair use rationale to "defend" Wikipedia itself from liability, it should not be relied upon exclusively for the same reasons that content restricted to non-commercial use is banned. We want our content to be reusable by others, so avoid using higher resolution images than necessary, make sure images are directly relevant to the article, and don’t use more images that you have to, and so on.