Why is the product image not showing in Woocommerce emails?

Question

WooCommerce

Hello,
email-order-details is set to 'show_image' => true, but the image is not displayed in emails to the client, what could be the reason?

<?php
      echo wc_get_email_order_items( $order, array( // WPCS: XSS ok.
        'show_sku'      => $sent_to_admin,
        'show_image'    => true,
        'image_size'    => array( 100, 100 ),
        'plain_text'    => $plain_text,
        'sent_to_admin' => $sent_to_admin,
      ) );
      ?>

Thanks for the help.