themes-wordpress/libretto/js/keyboard-image-navigation.js

jQuery( document ).ready(function($) {
	$( document ).keydown(function(e) {
		var url = false;
		if (e.which == 37) { // Left arrow key code
			url = $( '.previous-image a' ).attr( 'href' );
		} else if (e.which == 39) { // Right arrow key code
			url = $( '.entry-attachment a' ).attr( 'href' );
		}
		if (url && ( ! $( 'textarea, input' ).is( ':focus' ))) {
			window.location = url;
		}
	});
});