Purpose of the Copyright Symbol
Knowing how to copyright a photograph or other artistic work that has been edited or created in Photoshop is important for any artist.
Fortunately, all original works of art are copyrighted from inception. Prior to 1989, a copyright notice was required on all published works of art in order to claim copyright, however, that requirement no longer exists. However, there are still benefits to publishing a copyright notification with your original works.
A properly published copyright notice is important because it informs those viewing the work that it is protected by copyright. It also informs viewers who the copyright owner is, which can be useful when someone wishes to purchase some form of rights to republish your work. Most importantly, if a copyright is ever infringed, a proper copyright notice eliminates the ability of a defendant to claim an "innocent infringement" of the work. Damages for willful infringement are much higher, and thus eliminating the claim that infringement was not innocent makes it both more likely that a defendant might settle for a larger amount, and makes it more worthwhile for the artist to fully litigate the matter.
The notice for all "visually perceptible copies" of a work requires three elements. These elements include the name of the copyright holder, the year of first publication of the work, and the copyright symbol, which is the letter C inside of a circle.
In other words, to attach a proper copyright notice, you need to know how to type the copyright symbol in Photoshop CS4.