// 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 = '' . $product->get_image(array(48, 48)) . '';
        $item_name = $product_image . $item_name;
    }

    return $item_name;
}