Its extremely difficult to stop people from using your © materials online or off.
You could use a tool like
https://www.copyscape.com/online-copyright-protection/
You could also use, from $99
https://www.trademarkengine.com/services/copyright-registration?gclid=EAIaIQobChMIz_ioz5LM3AIVCMNkCh1 z6AzjEAAYASAAEgJHNPD_BwE
But in almost 50 years of shooting porn i have yet to find anything that works 100%