Open admin/super_packingslip.php. Find this block of code:
Code:
  // Add product images if there are 3 or less products on order
  if (sizeof($order->products) < 4) {
    $display_images = 1;
  }
  else {
    $display_images = 0;
  }
Right after this add the following line:
Code:
  $display_images = 0;
Voila.