Image optimization is an art that when mastered, the users of your website will notice.
There is a lot of information in your .png/.jpg/.gif files that you can get rid off by just using smush.it, an amazing tool developed by Yahoo.
Smush.it will remove metadata, correction codes and other stuff that is just unnecessary, without changing the original quality.
You should include smush.it in your build/deploy process. Also, if you have your images in a directory tree, you can have some kind of cron job that optimizes the images of your web application.
Try it here: http://www.smushit.com/