Insert this:
Code:
{include file="product_thumbnail.tpl" productid={$products[prod_num].productid image_x=$product.image_x image_y=$product.image_y product=$product.product tmbn_url=$product.tmbn_url id="product_thumbnail"}
into your order_info.tpl file within the {section name=prod_num loop=$products} loop where you would like it to show up.