<?php if( !empty($thumb) && isset($thumb) ){
$thumb = wp_get_attachment_image_src(get_post_thumbnail_id($post->ID),'');
?>
<div class="innerImage" style="background-image:url(<?php echo $thumb[0]; ?>)">
</div>

<?php } else { ?>
<div class="innerImage" style="background: url(<?php echo $mts_options['dm_inner_image']; ?>) no-repeat center center / cover;"></div>

<?php } ?>