[chris24]

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).

[icoloma]

You can use a title attribute that displays the shortcut. Desktop applications (such as GIMP) do that all the time

[mehulkar]

wouldn't that translate into a swipe?