WC_Product::get_image_id PHP Method

    public function get_image_id($context = 'view')
    {
        return $this->get_prop('image_id', $context);
    }

 /**
  * Get the images for a product or product variation.
  *
  * @param WC_Product|WC_Product_Variation $product Product instance.
  * @return array
  */
 protected function get_images($product)
 {
     $images = array();
     $attachment_ids = array();
     // Add featured image.
     if (has_post_thumbnail($product->get_id())) {
         $attachment_ids[] = $product->get_image_id();
     }
     // Add gallery images.
     $attachment_ids = array_merge($attachment_ids, $product->get_gallery_image_ids());
     // Build image data.
     foreach ($attachment_ids as $position => $attachment_id) {
         $attachment_post = get_post($attachment_id);
         if (is_null($attachment_post)) {
             continue;
         }
         $attachment = wp_get_attachment_image_src($attachment_id, 'full');
         if (!is_array($attachment)) {
             continue;
         }
         $images[] = array('id' => (int) $attachment_id, 'date_created' => wc_rest_prepare_date_response($attachment_post->post_date_gmt), 'date_modified' => wc_rest_prepare_date_response($attachment_post->post_modified_gmt), 'src' => current($attachment), 'name' => get_the_title($attachment_id), 'alt' => get_post_meta($attachment_id, '_wp_attachment_image_alt', true), 'position' => (int) $position);
     }
     // Set a placeholder image if the product has no images set.
     if (empty($images)) {
         $images[] = array('id' => 0, 'date_created' => wc_rest_prepare_date_response(current_time('mysql')), 'date_modified' => wc_rest_prepare_date_response(current_time('mysql')), 'src' => wc_placeholder_img_src(), 'name' => __('Placeholder', 'woocommerce'), 'alt' => __('Placeholder', 'woocommerce'), 'position' => 0);
     }
     return $images;
 }