@hube2 , hi trying to do this to apply a class to woocommerce single product gallery thumbnails. i’m using a true/false acf field on media attachment.
this code is not working for me:
<?php
$image = get_field('quick_ship');
$size = 'full'; // (thumbnail, medium, large, full or custom size)
if( $image ) {
echo wp_get_attachment_image( $image, $size, array ('class' => 'quick-ship' ) );
}