That's certainly the easiest way.
Another way is to be sure that your comic is in the middle of your screen. Then you want to hold control and press the button that says "Print screen" (or perhaps a shortened version such as "Prt Scr"). This will copy the image of whatever is currently on your screen to your clipboard. The way I understand it, Mac users have a different way to do this, so if you have a mac, consult another mac user. Once you have the image copied, open MS paint. At the top, go to the "Edit" tab, then to paste.
You should then see the screen you previously saved. Next you'll want to crop the image until only the comic is on the screen. Then you can save it so that you can post it other places on the internet.
It's a lot of work, but hopefully it serves your purposes.
Mediocrity at its most average.