new editors claiming copyright

Hi

We get this all the time: 
1. New user (or anon) copies text onto wikipedia that is identical to text on 
another website.
2. The RC "police" replaces the page with a copyvio notice.
3. The user claims that they are the copyright owner.

Is there any standard procedure to verify that they are indeed the copyright 
owner? What is deemed sufficient proof: Simply their word? A replied email to 
the webmaster of the relevant site? 

Thanks,
Sascha Noyes
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