Tim Thumb replacement

Hi there
I manage a site that has a built in blog at https://www.whileoutriding.com/blog
After a recent update of the twenty twelve theme on what it’s based plus a wordpress core update, the thumbnails on each summary intro on the blog page have disappeared (I am using a child theme I hasten to add!).
They were being displayed using the dreaded timthumb with the following code in the content.php document:

<?php if ( !is_single() ) : // Only display Excerpts  ?>
<?php
if ( function_exists( 'get_the_image' ) )
$get_the_image_as_array_feature = get_the_image( array( 'image_scan' => true,
'format' => 'array','default_size' => 'full' ) );
$the_img_src = $get_the_image_as_array_feature[url];
if(!empty($the_img_src)) {
?>
<a href="<?php the_permalink(); ?>">
<img src="https://www.whileoutriding.com/timthumb.php?w=150&h=150&zc=1&src=<?php echo $the_img_src; ?>" class="Thumbnail thumbnail custom-image" /></a>
<?php } ?>
<?php // get_the_image( array( 'image_class' => 'custom-image', 'image_scan' => true ) ); ?>

I have searched for some help on this either by using another bit of code or something now built into WordPress but my coding ability is very limited..

Any help would be very much appreciated.

thanks
Kevin