One of the things we'd love to be able to do is provide this feature for everyone, including people who don't have a subscription. The reason why we can't is that hosting images is one of the most expensive parts of running the website, and Line of Action doesn't have the resources to provide uploads for free to all. The subscriptions currently help cover the basic expenses of running the site, but it's unfortunately not enough to do much more beyond that without making the site admin pay out of her own pocket to cover the additional costs.
We really want to, but we can't without causing financial distress. I hope this helps explain it!