If you received this message from Google Adsense, then you have committed Copyright Infringement.
Google is serious about copyright infringement as it complies to the Digital Millennium Copyright Act (DMCA).
How do I report a site using my content?
If you believe that a site which is participating in the AdSense program is displaying your copyrighted material without the rights to do so, please report it using this form or by clicking on the AdChoices icon.
How to resolve this problem
The only solution which I would recommend is to remove all copyright related materials from your website.
If the copyright is on an image on your site, you can scrape off metadata from the image to remove the copyright information. Use this tool to remove metadata from any image.