To have a copyright in your webcomic, you don't need to do anything beyond drawing the comic. However, you can formally register your copyright with the U.S. Copyright Office for additional legal protection. Because of the online and community aspects of webcomics, you might also consider a Creative Commons license for your work.
Copyright attaches to an original creative work the moment it is fixed in a tangible form. Depending upon your work process, you might have a copyright in your webcomic after you first sketch it out on paper or after finishing it in a software program. You don't have a copyright in the webcomic when it is just an idea in your head. The copyright gives you the exclusive right to distribute, display, copy, sell and make derivative works based on your webcomic. You can license any or all of your exclusive rights to other people.
If you want to be able to sue someone for infringing on the copyright in your webcomic, you must register your work with the U.S. Copyright Office. You can register on the Copyright Office’s website or by submitting paper forms. As of the date of publication, the registration fee varies, depending on what and how you register. Online registration of a single work is $35. If you register your webcomic prior to someone infringing your copyright, or within three months of obtaining the original copyright, you can sue the infringer for statutory damages. Otherwise, you can only sue for your actual damages.
Many online users like to share and modify the works they find on the Internet. This sometimes allows communities to grow. If you opt for a Creative Commons license, you can set standard terms by which others can share and use your webcomic. You have many options from which to choose, including not allowing anyone to modify your comic and not allowing distribution of your comic for commercial purposes. A Creative Commons license does not modify your underlying copyright; it only grants other people a license to use your work under the limited circumstances you have determined are acceptable to you.
You own the copyright in your webcomic for your lifetime. After you pass away, your heirs will own the copyright for an additional 70 years. At the end of that time, your webcomic passes into the public domain for anyone to use. Under current law, this protection for the full-length of the copyright term is automatic and requires no action on your part. You don't have to use a Creative Commons license for your webcomic or grant anyone the right to use your webcomic for any purpose. Because your copyright is exclusive, the choices are entirely yours to make.