MediaWiki Administrator's Handbook/How to Handle Copyright Violations
Copyright Violations -- usually referred to as "Copyvios" for short -- occur when copyrighted text or files are added to a wikimedia project. How this is dealt with depends on the type of material that was copied.
Wikimedia projects are copyrighted using the GFDL. Some other copyrights are compatible with the GFDL for images and other files.
Copyrights that restrict the use of materials for any purpose are incompatible with the GFDL, and so including them in a GFDL document results in a violation of the material's copyright.
All images uploaded to wikimedia projects must have their copyright status announced using one of the provided templates.
Public Domain, GFDL, and most Creative Commons licences are permitted.
"Fair Use" images are permitted on some projects, but not others.
These can be harder to ferret out.
Text that is copied and pasted from other websites is the most common problem. In many cases the user who contributed the material will add a link to the source website. Most users are not familiar with how the copyright laws apply, so they should be dealt with kindly (but firmly).
Text from printed materials is less common, but much harder to catch.
Text copied from other wikimedia projects can be very difficult to catch.