Radical Comic Designer for Linux allows you to quickly, and easily, design your own comic strips and comic books. Radical Comic Designer includes everything necessary to create your own web comics!
Start by adding panels to your page. Then drop your favorite pictures onto the panels. (You can double click on the pictures within in panels to edit them.) Add a few Speech Bubbles, and boom. You've got your very own comic.
When you're done designing, you can export to a picture for posting on your website. In addition you can save to the standard CBZ file format (which can be read by RadicalCodex).