image 'size' not working with 'image_scan'

Hi all, this is a great plugin but i seem to be stuck with 1 little part…
I am using the Twenty Twelve theme but it’s only in my localhost at the moment so i can’t give an address to look at the site, but I have the get_the_image function in my ‘content.php’ file in the section for “Only display Excerpts for Search”, as below…

<?php if ( is_search() || is_archive() ) : // Only display Excerpts for Search and Archive ?>
<div class="entry-summary">
 <div class="excerpt-thumb">

<?php if ( function_exists( 'get_the_image' ) ) {
  get_the_image( array(
    'size' => 'thumbnail',
    'image_scan' => true
  ) );
} ?>

 </div>
<?php the_excerpt(); ?>
</div><!-- .entry-summary -->

The problem is that the images that are inserted from the actual post content ('image_scan' => true) are not displayed as the thumbnail ('size' => 'thumbnail').

Other images that are from the posts Featured Image are correctly displayed as the image thumbnail.

Am i doing something wrong with the code to get it to display the thumbnail of an image within the post, or do i have to do something else like add ('width' => '150') & ('height' => '150'), which would squash some images as they are not perfectly square in shape, so is not ideal.

Hope someone can help.
Thanks,
Ian

https://www.ads-software.com/plugins/get-the-image/