They are already copyrighted since you made them. They are copyrighted just like software. Just be sure you have proof that you made them in case you should have to prove they are yours.
What Works Are Protected?
Copyright protects “original works of authorship” that are fixed in a tangible form of expression. The fixation need not be directly perceptible so long as it may be communicated with the aid of a machine or device. Copyrightable works include the following categories:
http://www.copyright.gov/circs/circ1.html#wwp
literary works;
musical works, including any accompanying words
dramatic works, including any accompanying music
pantomimes and choreographic works
pictorial, graphic, and sculptural works
motion pictures and other audiovisual works
sound recordings
architectural works
These categories should be viewed broadly. For example, computer programs and most “compilations” may be registered as “literary works”; maps and architectural plans may be registered as “pictorial, graphic, and sculptural works.”
