<?php

global $post;
$captions = array();

echo "<div id=\"slider\" class=\"nivoSlider\">";
$args = array(
    'numberposts' => '-1',
    'orderby'         => 'menu_order',
    'order'         => 'ASC',
    'post_type'       => 'slider_image' );



$images = get_posts($args);

for($i=0; $i <= count($images);$i++){

if($images[$i]->post_title != ''){
echo get_the_post_thumbnail($images[$i]->ID, 'full', array( 'title' => "#caption".$i+1));

array_push($captions, $images[$i]->post_title);


}
else
{
echo get_the_post_thumbnail($images[$i]->ID, 'full');
}

}

echo "</div>";

print_r($captions);
$count = 1;
foreach($captions as $c => $v){

echo "<div id=\"caption".$c++."\" class=\"nivo-html-caption\">";
echo $v;
echo "</div>";

count++;
}

?>