Newer browsers (IE8, Chrome) have upped the max number of connections per server to 6 which is a good trend.
However, to get around the 2 connection limit (without requiring a browser config change) a trick you can use is to create multiple CNAMES (aliases) in dns that point to your web server. Then in your app you generate the image tags with patterned (or random) HREFs that utilize all of your. This tricks the browser into thinking that the images are coming from different sources and then will open more than 2 connections to your site at one time. This won't necessarily help your serve time for a single image, but for your overall page load time it should provide you some relief.
You would need to consider a couple of things before employing this technique:
- How this would work with your application's caching mechanism. You might end up with a much larger cache of your images
- You would need to pay attention the number of concurrent connections on your web server as it'll go up as the number of concurrent sessions remains the same
There are a ton of posts are there that explain this technique in detail. Here is a good one from DevCentral:
The third greatest (useful) hack in the history of the Web