- How to sort and categorize images
Other people need to find your file in order to use it to illustrate articles in other Wikimedia projects, so it is crucial to add your media files to specific categories. Every image must be in at least one classification category; otherwise your valuable media files won't get used as much as they could be.
If you wish, you may also add them to specific gallery articles on Commons. An example of a gallery page could be the image gallery of the planet Mars.
You can tell if a page is an article or a category by looking at its name. Pages without a prefix are article pages, pages with a "Category:" prefix are categories and pages with "File:" are File pages (images, sound or video). This concept (implemented with these prefixes) is called "namespaces". That way you can easily identify different content types by their namespace prefix.
Adding images to categories
Adding an image to a category is done like adding a Wikipedia article to a category. Simply place something like the following example code at the image page itself:
[[Category:Some specific category]]
Be as specific as possible. Don't add an image to an overcrowded root category. In order to find a right category for your image, the category tree function will help you a lot: just go to a general category, such as Category:Countries and then follow the subcategories until you find the most specific one that describes your image.
Adding images to galleries
In order to add an image to a gallery go after upload to the gallery article, click there on "edit" and you will see among other things something like this:
<gallery> Image:Mars Valles Marineris.jpeg|Valles Marineris on Mars Image:Mars Hubble.jpg|Mars seen by the Hubble Space Telescope, Realistic Colors </gallery>
Which looks like:
You can add your image between those two gallery-tags (one opening and one closing tag) in the following way:
Image:Your photo name.jpg|A brief description
Wolfgang Amadeus Mozart - Don Giovanni - Overtüre
In addition to subject categories, it is helpful to add categories indicating software or equipment used in making the file, such as:
Wikimedia Commons pages: