Disclaimer: I am not an attorney. End of disclaimer.
Now for the unvarnished truth…
Registering a Copyright does not prevent the theft of a photograph. Cash, lots of cash, will stop the theft of a photograph. I had the unpleasant experience of learning this the hard way; I spent three years in a nasty and expensive legal battle fighting for my intellectual property rights. Fortunately, I won my case, however, that is not always guaranteed.
I Copyright my photographs and so should you. If I do not, and a photograph is stolen, I would not be able to file a lawsuit; the court will dismiss it. Therefore, registering a Copyright is the first step and I strongly suggest hiring an attorney to help explain the process. Read more about Copyrights at the U.S. Copyright Office: https://www.copyright.gov/
Some copyright infringements are accidental, innocent or unintentional; in fact, most people do not know about an artist’s rights or they think their use is allowed. Most people, when confronted, will correct an infringement immediately without the need for litigation. If you discover one of your photographs being used without authorization, hire an attorney. A simple cease and desist letter might be all that is necessary; it might cost as low as $500 (this is what I meant by cash). If ten different people steal a photograph, and if each case is slightly different and requires time, it may cost $5,000 (10 X $500, hence, lots of cash).
In my lawsuit, the defendants were nauseating spiteful people who were upset with being caught and did not feel my work had any value (although they did steal it); they fought back and lost. I do not recommend litigation; in addition to the financial burden, there is an emotional cost too. Worse, you may not win, and you may have to pay the legal fees of the defendant. Get a realistic perspective from an Intellectual Property attorney (do not hire a real estate or divorce lawyer for copyright matters). In my case, the defendants spent considerable efforts to invalidate my copyrights on technicalities, however, the judge was not convinced. After the case was over, I was left with a mountain of paperwork, tens of thousands of pages of legal briefs and motion replies; it was cathartic to burn them.
Copyright law is complex; while designed to protect the artist’s rights, it also permits fair use in certain circumstances. Further complicating the matter are agreements you may enter into by using social media websites such as Instagram or Facebook i.e. the Click I Agree agreement. Read more here and here.
Should you worry? Should you lose sleep at night or get angry? In my opinion, no. Learn how to Copyright photographs and enjoy sharing them with everyone. It is not the end of the world if one of your photographs is used by someone else, do not let it ruin your life (I say that from experience).