Once you have established that you own the copyright in the content, send a DMCA takedown notice to the website. Many sites make a DMCA takedown webform available for your use. You may feel free to use such a form. Pinterest has an exemplary DMCA takedown webform.
Use clear and accurate language in takedown requests that carefully follows the DMCA notice elements set forth in 17 U.S.C., Section 512(c)(3). We have provided a sample takedown notice that you may feel free to adapt to your situation: Sample DMCA Notice.
Please note that the person who posted the content may receive a copy of your DMCA notice, including your contact information and any other information you may have included in the notice. If you are not comfortable divulging, e.g., your street address to the user you are filing against, consider using a post office box in place of your home or office address and/or authorizing a third party to file on your behalf. The third party doesn’t need to be a lawyer; any person may be authorized to act on behalf of the copyright owner in sending a DMCA notice. For additional ideas, see 5 Ways to Protect Your Privacy When Sending DMCA Notices, Plagiarism Today (Aug. 19, 2014).
Most websites will comply with valid DMCA takedown notices because if they don’t, they risk being sued and liable for copyright infringement.