Wikimedia Commons

Wikimedia Commons is a repository of free media files created and maintained by the wiki community - unassociated individuals - rather than an organization. The Commons was created for storage of media used in other wiki projects: like Wikipedia, Wikisource, and Wikibooks. However, as long as you give credit to the authors, you are free to copy, use, and modify all of the media on the site for any other projects - including commercial projects. Interestingly, the site itself says that there are many images on it that are not and will never be used anywhere else.

Collection Principles
By definition, wikis are constantly evolving, so a collection development policy exists, but may be different tomorrow than what is was today. Right now the repository focuses on media that could be potentially useful on other wiki projects, so already that's pretty subjective. The media must be free, and Commons community members are constantly on the lookout for material that needs to be deleted, either through a standard deletion process or by "speedy deletion." Deletions are necessary when there are copyright violations, duplications, poor quality, and incorrect naming. Oftentimes, wikis are not very well organized, and much of the information about collection principles, copyright, deletion guidelines, etc. took a bit of hunting to find. The place where Commons shines is, of course, its broad accessibility. Also, I think Commons goes beyond merely fitting into the larger context of the wiki world because it offers media for an infinite amount of other uses as well.

Metadata
Though I didn't log in and don't know exactly what options the uploader has for providing metadata, I can see from browsing around that all images have Description, Source, Date, Author, Permission, and License information. Additionally, some images have an Original Upload Log and File History. You can see a list of webpages that link to the file. Also, some images have a section titled Metadata that seems to contain the technical metadata embedded in the media file.

Object Characteristics
Since the objects in this collection are contributed by individuals, there are no rigid standards for size, file type, documentation, etc. of the media objects. Though the website offers recommendations for supplying the highest quality objects, the only control the community has for quality is the members themselves. Quality can only be maintained by the "neighborhood watch group."

Audience
My guess is that the audience for Wikimedia Commons originally was intended to be the contributors and consumers of other wiki projects. It seems, though, that the audience has expanded to be anyone who wants to publicly store high quality media and anyone who wants to copy, use, and edit free high quality media.