Use a callback on the scroll event:
http://jsfiddle.net/isherwood/yX5vr/36
$('.carousel-stage').on('jcarousel:scrollend', function(event, carousel) {
$('.wrapper h1').text( $(this).jcarousel('visible').find('img').attr('alt') );
});
http://sorgalla.com/jcarousel/docs/reference/events.html#scrollend
To get the initial title, add this somewhere after your init:
$('.wrapper h1').text( $('.carousel-stage').jcarousel('visible')
.find('img').attr('alt') );