Robo Pastierovic has created Advanced Comic Book Format (ACBF), a free/open format for online comic books. ACBF has a lot of cool features: support for creator metadata; per-panel/page definitions; multiple text-layers for multiple languages; text formatting and style data; auto-indexing and more. The format is CC-BY-SA, and can be found on Launchpad, along with GPL’ed viewers for GNU/Linux and Windows.
There’s screenshots, too. Robo was kind enough to convert the comic adaptation of my story Craphound, which appeared in my CC-licensed graphic novel Cory Doctorow’s Futuristic Tales of Here and Now — he also translated the comic into Slovak and included the translation in a separate layer.