https://github.com/zecka/pictifly

pictifly-config-regeneration.php

<?php

// attach a post type to pictifly regeneration
add_filter('pf_post_type_regenerate', 'prefix_pf_post_type_regenerate', 1, 1);
function prefix_pf_post_type_regenerate($post_types){
    $post_types=['custom_type'];
    return $post_types;
}
// Create custom method to regenerate image
add_action('pf_post_images_regenerate', 'prefix_pf_post_images_regenerate',10, 2);
function prefix_pf_post_images_regenerate($post_id, $post_type){
    global $_pf_regenerated_imgs;
    if($post_type=="custom_type"){
        $thumb_id = get_post_thumbnail_id($post_id);
        if($thumb_id){
            $_pf_regenerated_imgs[] = pf_get_simple($thumb_id, 200, 200, true);
        }
        $images = get_field('images', $post_id);
        if($images){
            foreach($images as $image){
                $_pf_regenerated_imgs[] = pf_img($image, "custom_size", false);
                $_pf_regenerated_imgs[] = pf_get_simple($image, 200, 200, true);
                $_pf_regenerated_imgs[] = pf_get_simple($image, 400, 400, true);
                $_pf_regenerated_imgs[] = pf_get_simple($image, 600, 600, true);
            }
        }
    }
}