WordPress | Set ACF image to be the WP feature image

acf_image_to_featured_image.php

<?php
/**
* Because WP does not allow us to set minimum image dimensions on upload we often
* use an ACF image. However this means within the dashboard we lack a thumbnail
* Here we set the ACF image to be the WP thumbnail. 
*/
function image_to_thumbnail( $post_id ) {
    if( get_post_type($post_id) != 'talent' ) {
        return; // Stop if post-type is not talent
    }
    $featured_image = get_field('featured_image', $post_id);
    if( $featured_image ) {
        $attachment_id = $featured_image['ID'];
        set_post_thumbnail( $post_id, $attachment_id );
    }
}
add_action( 'save_post', 'image_to_thumbnail' );