Edit: Looks like you need to maintain a reference to the api when you add jcrop to an image.
// assign jcrop to jcrop_api
var jcrop_api = $.Jcrop('#imgThumbnailer', {
onChange: statusCrop,
onSelect: statusCrop,
bgColor: 'black',
bgOpacity: .3
});
// when you want to remove it
jcrop_api.destroy();