{assign var="final" value=0 scope=root}
{foreach from=$products item=product}
  {$final=$final+1}
    <div class="order-line row">
      <div class="col-md-2 col-md-4">
        <span class="image">
          <img src="{$product.cover.medium.url}" />
        </span>
        {assign var="id{$final}" value={$product.cover.medium.url} scope=scope}

{foreach from=$products item=product}
  {$i=$i+1}
    <div class="order-line row">
      <div class="col-md-2 col-md-4">
        <span class="image">
          <img src="{$id{$i}}"/>
        </span>
      </div>