Sorry all for the long wait times! Was not expecting much interest. At the very least, I need to look into removing photos from the queue when people exit the page.
Done - upgraded to a t3.xlarge. Now it can process 4 images in parallel. Still not enough to keep up with HN demand, but it should chew through the queue a _bit_ faster.
Unfortunately nothing at the moment! Currently working on removing images from the queue if the user has left the page (which I'm guessing is the case for about 99% of the current queue).