What could I do to stop other people from using my work?

Have an IP attorney send them a cease and desist letter.

As a copyright owner, you have the exclusive legal right to print, publish, perform, film, or record literary, artistic or musical material and to authorize others to do the same. Your registration provides you some additional procedural advantages including a presumption of validity and attorneys fees. In this instance, it is not clear from your narrative: (1) whether your photograph is being used by others, or (2) whether a hair style (or some other object) depicted in the photograph is being used by others. Copyright only protects the first scenario. So, if there is unauthorized use of your photograph, you need to have a cease-and-desist letter prepared and sent to the infringers. We would be delighted to advise you regarding your specific facts and all possible legal strategies and remedies. As always, you should consult with an intellectual property or Copyright attorney to explore all of your legal remedies before proceeding.

You need to hire a copyright lawyer. The attorney will send a demand letter to in infringer's requesting they stop - or they will be sued. You can really do nothing on your own in this situation. You could even harm your case if you try. GOOD LUCK!

Send each person using your photograph without your permission a "cease and desist" letter informing them that your images are both copyrighted and registered with the U.S. Copyright Office. Insist that they stop using the photographs and remove them immediately from every place and in every medium they have placed the images. Tell them that if they continue to use your photographs without permission, you will file suit in federal court naming them as defendants and describe the penalties established by statute. Do not threaten them in any manner. An attorney with experience in intellectual property law can help you.