Using the left/right keys is a great idea, but you'd have to have some clever way of making users aware of it.
You'd also have to come up with a solution that works on devices that don't necessarily have a keyboard available at all times (on iOS, for instance).
You can use a title attribute that displays the shortcut. Desktop applications (such as GIMP) do that all the time
wouldn't that translate into a swipe?
It's not always possible to place pagination links at the same location if the webcomic has images of different sizes, but I have yet to see a physical keyboard that moves around depending on what's on the screen.