The problem is you are triggering functon on $('.b-r')
instead of $('.b img')
$(document).ready(function () {
$('.b img').jrumble({
x: 2,
y: 2,
rotation: 1,
speed: 75
});
$('.b-r').hover(function () {
// here $(this) refers to $('.b-r')
$('.b img').trigger('startRumble');
}, function () {
$('.b img').trigger('stopRumble');
});
});