// $fields['immagine']['raw_value']; => /var/www/miosito/web_dir/wp-contents/upload/mia_img.gif
// $post_id è il post a cui collegare questa immagine tramite ACF

$file = $fields['immagine']['raw_value'];
        $filename = basename($file);

        $upload_file = wp_upload_bits($filename, NULL, file_get_contents($file));
        if (!$upload_file['error']) {
          $wp_filetype = wp_check_filetype($filename, NULL);
          $attachment = [
            'post_mime_type' => $wp_filetype['type'],
            'post_parent' => $post_id,
            'post_title' => preg_replace('/\.[^.]+$/', '', $filename),
            'post_content' => '',
            'post_status' => 'inherit'
          ];
          $attachment_id = wp_insert_attachment($attachment, $fields['immagine']['raw_value'], $post_id);
          if (!is_wp_error($attachment_id)) {
            require_once(ABSPATH . "wp-admin" . '/includes/image.php');
            $attachment_data = wp_generate_attachment_metadata($attachment_id, $upload_file['file']);
            wp_update_attachment_metadata($attachment_id, $attachment_data);
            zbl_log($attachment_id, FALSE, "file caricato");
            update_field('servizio_immagine', $attachment_id, $post_id);
          }
          else {
            zbl_log($attachment_id->get_error_message(), FALSE, "Errore in wp_insert_attach");
          }
        }
        else {
          zbl_log($upload_file['error'], FALSE, "Errore in upload_file");
        }

        wp_update_post($post_id);