Wikipedia:10 things you did not know about images on Wikipedia

This image is free, so I can use it here and you can use it too!
10 things you did not know about images on Wikipedia is a list of insights about Wikipedia specifically targeted at people who have limited foreknowledge about images on the project, such as new editors and new readers. These explanations should not surprise experienced editors, but hopefully will help the rest of the world to shape an informed opinion of our work and understand why sometimes it seems we do not have an "easy to get image" of something.
1. We want images.
However, we primarily want freely licensed images which are compatible with our policies and goal of creating a free resource for everyone. If a picture is worth a thousand words, a free one is giving a thousand words to everyone who wants to use it and will ever see it; a non-free one only gives visitors to this single website a thousand words.
We depend on people like you to author and contribute images for Wikipedia, and the rest of the world, to use, as long as you are willing to release the images under a free license.
When we say freely licensed we're talking about the freedom of use the public has with images, not the price.
More information: Wikipedia:Requested pictures, The Definition of Free Content
1. We want usable images.
Please do not upload images that should not or can not be used in an article. While we permit a limited amount of images for users to use on their user page, we do not need a 9th image of your Jack Russell Terrier on that article. The Wikimedia Foundation is not a free webspace for your images. Please use a website designed for this.
2. We have 750,300 images.
We reached 1 million images on all Wikipedia projects in July of 2006. There are over 1.75 million images on Commons. On the English Wikipedia we have over 750,000 images. You can help Wikipedia by going through images and looking for problems such as missing source and licenses. You can nominate images for deletion via IFD. You can cleanup images too; see Wikipedia:Images for cleanup.
More information: Special:Statistics, Commons:Special:Statistics, Special:Unusedimages.
3. All images uploaded must have a source and license.
Failure to provide a source (who made it) and license (how it can be used) will result in the image being deleted, possibly as soon as 48 hours. You must provide this information for all images uploaded. No ifs, ands, or buts about it. You must provide this information for all images you upload, with no exceptions, or the images will be deleted. Blatant and completely unjustifiable violations of copyright law and our image policies can be (and are) deleted almost immediately.
We have a long term mission to create and promote content which is free of the typical encumbrances of copyright law. This mission requires us to take copyright very seriously. Unlike (most) other websites that allow user submission and generation of content, we aggressively remove all copyright infringements as soon as we can find them and block people who willfully ignore this after being warned.
1. Because free content is a fundamental part of our mission our policy on image licensing is more restrictive than required by law.
More information: Wikipedia:Non-free content
4. Use non-free images only when nothing else is possible.
Do not go to the nearest website and grab an image of a person/place/building. It is extremely likely that image is both copyrighted and fails our Non-free content policy, which states that a non-free image may be used only when it cannot be replaced. For example, there's no way whatsoever that a logo of a political party or a screenshot of a video game can be replaced by a free image, but a photo of someone or a certain location can almost always be replaced, even if doing so may be very difficult. Search for free images, especially for living persons, existing buildings and places. Don't upload an image just because the article doesn't have one right now; we can (and will) wait for a free image to be created or released. If you are going to upload a non-free image, see Wikipedia:Non-free content criteria first. Wikipedia:Fair use rationale guideline will be helpful as well.
More information: Wikipedia:Non-free content criteria #1
5. Non-commercial, educational-only and non-derivative images are NOT "free" images.
All such restrictions unacceptably limit how other people may use the image off of Wikipedia, which completely contradicts the entire point of "free images" and "Free content" (See above). These licenses are not valid at all and such images must be justified as "fair use" or they will be immediately deleted.
6. No one has a perfect understanding of the copyright law.
Even if you are licensed attorney who practices in this area, US copyright law (which applies to Wikipedia) is complex, and while an understanding of how it applies to Wikipedia may be achievable, there is a considerable gray area and deciding the status of one image in a complex situation can be very difficult, if not impossible, at times.
7. We have an image use policy.
Once an image is uploaded and correctly sourced and licensed, it may then be used in articles. See Wikipedia:Image use policy, which describes the accepted ways of displaying, formatting, etc. images. If you use images in an article, you should be familiar with it. Example: Did you know ... that the largest an image can be displayed in an article is 550 pixels wide?
8. Ideally, there would not be any images stored on Wikipedia, they would all be on Wikimedia Commons.
Because we want free content, all images uploaded would ideally be free for everyone and therefore would be acceptable on our sister project, Wikimedia Commons. Images submitted to Commons are automatically available here... and on hundreds of other Wikis run by the Wikimedia Foundation. If you're looking for an image for an article, be sure to search using the commons Mayflower search.
More information: Wikipedia:Free image resources
9. Uploading the same image 8 times is not needed.
You can edit the image page! Just like every other page on Wikipedia, the image description page can be edited by anyone. Just click "edit this page" while looking at the image page. Forgot to license or give the source for the image when you uploaded it? Do not re-upload the image: edit the image description page and add the license!
Also, the wiki software can control the size of the images, so you do not need to re-upload a smaller version of the same image. See Wikipedia:Extended image syntax. There, you can learn how to use frames, control the position in the article and about captions! For more on captions, see Wikipedia:Captions.
10. You can use (free) images on Wikipedia yourself, anywhere you like.
You can use images that are on Commons and free images on Wikipedia provided you comply with the individual image license terms, not (necessarily) the GFDL. While all articles text are licensed under the GFDL, free images have several licenses to choose from. See Wikipedia:Image copyright tags/Free licenses for the many possibilities. You can use them on any page on Wikipedia. You can even use them OFF Wikipedia, such as on a website, printed material, anywhere! All "Free" image licenses allow these uses.
1. You cannot use non-free images anywhere except in relevant encyclopedia articles.
Non-free images can only be used in the article namespace where they have a rationale for existing. You cannot use them anywhere else, such as on policy pages, discussion pages, templates, or user communication pages. If you need to discuss them, link to them by putting a colon (:) between the "[[" and "Image:" like this: [[:Image:Imagenamegoeshere.ext]]

More information: Wikipedia:Non-free content criteria #9
[edit] Other media
All the above applies to audio and video too.
We allow other forms of media, such as audio and even video. The same rules apply for these media as they do for images.