How to copyright your work

From Legalzoom.com:
How to copyright your work

When you write a blog post, you instantly create a copyrighted work. According to the U.S. Copyright Office, your original work receives copyright protection “the moment it is created and fixed in a tangible form that it is perceptible either directly or with the aid of a machine or device.” In other words—you wrote it, you own it. This also applies to photographs and images—once a photograph that you took or image you created is fixed in a tangible medium, the copyright is yours instantly—no registration necessary, and no little © required.

However, there is one big “but”—if you want to sue someone in federal court for copyright infringement, your work must first be registered with the U.S. Copyright Office.