One or more over-enthusiastic and ill-informed (or malicious) authors who adds content to your wiki that they don't have the right to add can become a serious problem for your wiki. Their behavior, if it is not countered swiftly, can become an epidemic, or make other wiki users feel uncertain and lose trust in the wiki and they may become unwilling to continue contributing. You or your organization may even get sued, especially if the wiki is visible to the global Web.
Any of these symptoms may indicate you have a copyright infringement problem:
To make sure that you really have this problem, cut-n-paste unique expressions from the wiki's new material into a search engine. If there is a copyright infringement, it is very likely that you will find one or more source documents, which are neither public domain nor share-alike.
This problem should primarily be prevented with educating the wiki users. The wiki itself can serve as an important education channel: you can, for example, make sure that everyone who edits content gets a warning about posting copyrighted material when they start editing a submission. You can also have one or more pages about copyright on the wiki or link to suitable pages elsewhere.
If a user makes this mistake, first clean up (delete the copyrighted material and note the reason for deletion in the page log). Then leave a message for the user(s) through the normal channels of your wiki (e.g. on their user talk page or via email). Make sure your message is constructive and gives links to the information the user may need to learn what copyright is and why it matters for your wiki.
Would be needed.