Customise post output

Your problem is related to the theme you are using. You can choose other way to do this. Create a new template files for this and leave out the title and use get_the_post_thumbnail( $post_id, $size, $attr ); to get the images for instagrabber.

In your other thread you are creating a new loop so im gonna use it here to demonstrate how you can achieve this.

<?php query_posts('post_type=images'); ?>
<?php if (have_posts()) : while (have_posts()) : the_post(); ?>

<div class="post-image" id="post-<?php the_ID(); ?>">"><?php echo get_the_post_thumbnail( get_the_ID(), array( 300, 300 ) );  ?></div>

<?php endwhile; ?>
<?php else: ?>
<h2 class="main-h2">Images</h2>
<h2>No Content</h2>
<?php endif; ?>

array( 300, 300 ) means the image will be 300×300 pixels

if you want to display the caption yo can use <?php instagrabber_image_caption(); ?>

If you dont have the image saved in featured or both (only content) you may have to get the image like this:
change this:

<div class="post-image" id="post-<?php the_ID(); ?>">"><?php echo get_the_post_thumbnail( get_the_ID(), array( 300, 300 ) );  ?></div>

to this:

<div class="post-image" id="post-<?php the_ID(); ?>">"><img src="<?php instagrabber_image_url(); ?>" width="300">
<p>
	<?php instagrabber_image_caption(); ?>
</p>
</div>