To display the thumbnail image in the order items on Order received page (thankyou), you will use:
// Display the product thumbnail in order received page
add_filter( 'woocommerce_order_item_name', 'order_received_item_thumbnail_image', 10, 3 );
function order_received_item_thumbnail_image( $item_name, $item, $is_visible ) {
// Targeting order received page only
if( ! is_wc_endpoint_url('order-received') ) return $item_name;
// Get the WC_Product object (from order item)
$product = $item->get_product();
if( $product->get_image_id() > 0 ){
$product_image = '<span style="float:left;display:block;width:56px;">' . $product->get_image(array(48, 48)) . '</span>';
$item_name = $product_image . $item_name;
}
return $item_name;
}
Code goes in function.php file of your active child theme (or active theme). Tested and works.