$query_options = array(
    'post__in'          => get_option('sticky_posts'),
    'meta_query'        => array(
                    array('key' => '_thumbnail_id')
                )
);

$stickies = new WP_Query( $query_options );

echo "<p>post_count is $stickies->post_count and found_posts is $stickies->found_posts</p>";

if( $stickies->have_posts() ):
?>
    <div id="slider">
    <?php while( $stickies->have_posts() ) : $stickies->the_post(); ?>
        <div>Slider content for <?php the_title(); ?> omitted</div>
    <?php endwhile; ?>
     </div>
<?php   endif;