When someone copies your original work, such as a book or a song, without your permission, that individual has infringed on your copyright. An infringer might take credit for your work or may even earn income from it. In the United States, your original work of authorship is protected from the moment a tangible copy exists, so even if you don't formally register your copyright, you still have the legal right to pursue infringers. If you have registered your copyright, you'll have even more legal powers to pursue infringers, including the right to sue for statutory damages.
Send a cease and desist letter. If you believe someone has infringed on your copyright, the first step is typically to send a “cease and desist” letter to the infringer. This letter notifies the person of your copyright claim and demands he stop using your work. You can also use this letter to demand lost profits and inform the infringer that you plan to file a lawsuit by a certain date if he does not comply with your demands. If you have a registered copyright, you can also state you will seek attorneys' fees and statutory damages as well.
If you find unauthorized copies of your work on the Internet, you can contact the infringer’s Internet service provider. Under the Digital Millennium Copyright Act, or DMCA, you can demand the infringer's ISP delete the infringed material from its servers or prevent it from being accessed by others. The “notice and takedown” provision of the DMCA requires you give the ISP proper notice when requesting a takedown. The notice must clearly identify your copyrighted work and the infringing material. You must also provide a statement that you are the copyright holder. The notice must include your signature and contact information.
File a lawsuit. Even if you have not registered your copyright, you still have the legal right to seek damages for your lost profits. For example, someone steals your song and uses it in a commercial – you can recover whatever the song is worth for that use. You may also recover the infringer's profits and get an injunction, which means the court stops the infringing conduct. If you registered your copyright, you can seek statutory damages, meaning damages awarded when actual harm cannot be determined, as well as attorneys’ fees.