User:Sage Ross (WMF)/finding free images

The internet is full of freely licensed and public domain images, and many of them can be put on Wikimedia Commons and added to Wikipedia articles.

For freely licensed images (and audio, and video), this almost always means the Creative Commons Attribution or Attribution-ShareAlike licenses. (Many people also release new works with a CC0 deed, which puts them directly into the public domain.) Any version of Attribution (BY) or Attribution-ShareAlike (BY-SA) license (from 1.0 up to 3.0, and probably any future versions as well) is acceptable for Wikimedia Commons. However, the Noncommercial and NoDerivatives variants are not considered free licenses. (footnote: Other Wikipedia-compatible free licenses include the Free Art License, the GNU Free Documentation License, and the GNU GPL, but these are rarely used for images, audio or video.)

Finding CC works
For Creative Commons licenses, the biggest trove of images is on Flickr. After you do a search on Flickr, you can go to the "Advanced Search" options (flickr.com/search/advanced) to limit your search to freely licensed works. To return only Attribution and Attribution-ShareAlike photos, select all of these options:
 * Only search within Creative Commons-licensed content
 * Find content to use commercially
 * Find content to modify, adapt, or build upon

A note of caution: some images on Flickr are not actually the work of the users who uploaded them. Commons cases include images of art objects, photos of video content, screenshots and other media, and memes (e.g., where original text is added to someone else's photo). In such cases, Creative Commons licenses are not valid. (Using such invalid licenses is known as "Flickr-washing".) Do not upload an image to Wikimedia Commons if you suspect that it is not wholly the original work of the Flickr user who shared it. Of course, the same applies to images you find elsewhere on the web.

Beyond Flickr, the CC Search tool (search.creativecommons.org) is a good starting point to find freely licensed images--as well as audio and video. It links to a number of separate services and collections where you can find Wikipedia-compatible works.

Open access scientific journals are another increasingly useful source of images. In particular, the Public Library of Science (PLoS) journals publish articles--and accompanying photos and diagrams--with the Creative Commons Attribution license. Try searching Google Scholar (scholar.google.com) with the added keyword "site:plos" to find useful scientific images.

Determing public domain status
The countless works in the public domain have no copyright restrictions, and can be used by anyone for any purpose. Public domain works include:
 * old works for which copyright has expired;
 * works that are ineligible for copyright (because they sufficient originality)
 * works created by some governments and other public institutions that are automatically public domain; and
 * works that have been explicitly released into the public domain by their creators.

Identifying public domain content can be much more complex, and they are rarely marked explicitly as public domain. There are some simple cases:
 * Works of the United States federal government
 * Works published in the United States before 1923
 * Works explicitly released to the public domain by their authors (including via a CC0 deed)

Beyond that, it gets complicated quickly. Outside the United States, published works become public domain in most countries 70 years after the author's death, although if a work was published 1923 or later, it might still be copyrighted in the United States. (Works must be public domain in the United States *and* their source country to be compatible with Wikimedia Commons.) Works published in the United States between 1923 and 1963 (inclusive) are in the public domain unless the owner filed for copyright renewal approximately 28 years after publication, but that is usually difficult to determine. Wikimedia Commons has several guides for determining the copyright status of a particular work:
 * The "Hirtle chart" for determining public domain status in the United States (for images and text only): commons.wikimedia.org/wiki/Commons:Hirtle_chart
 * The "International copyright quick reference guide" for determining the source country public domain status non-U.S. works: commons.wikimedia.org/wiki/Commons:International_copyright_quick_reference_guide

After you get confused trying to use those guides, you can post about specific works at the Copyright section of Commons' village pump discussion forum: commons.wikimedia.org/wiki/Commons:Village_pump/Copyright

Finding pubic domain works
Public domain works are spread out across the Internet, with more collections appearing all the time. Many libraries, archives, galleries and museums have rich collections of public domain works, often in searchable databases. You can browse the "free media resources" page on Commons to get a feel for where to look for potential public domain works: http://commons.wikimedia.org/wiki/Commons:Free_media_resources

Many public domain works are not available in digital form, but if you have access to something you'd like to use on Wikipedia (through a library or archive, for example), you can create a scan or photograph yourself and upload it to Wikimedia Commons.