If you're using a Windows PC, you can press the Print Screen button on your keyboard to take a screen grab of your comic, then load it into Photoshop or whatever, crop it, and save it as an image.
If you're using a Mac, you are already awesome, but if for some reason you aren't awesome, there is a program called "Grab" which allows you to make a selection of a certain part of the screen (your comic) to store and then print.
