I operate a website targeted to a very niche demographic where there is only one other competitor. This competitor has been doing it for years (my site is only a few months old). This competitor has been making some attempts to prevent my site from gaining traction (obviously because he doesn't want any competition). To indirectly get back at him, I purchased some Facebook social ads, and used a photograph that he was in to promote my site. Now he is sending emails to me saying that its illegal to do so, and is threatening legal action. He may or may not own the photograph that I am using. However, I asked him to produce documentation or a link proving it was his. He wouldn't but insisted that it is him in the photo (which i knew). Do I really have anything to worry about? Should I leave the ad up or take it down?