Belongs to Yahoo!, Smush.it is completely cloud-based image optimization tool.
Smush.it uses optimization techniques specific to image format to remove unnecessary bytes from image files. It is a “lossless” tool, which means it optimizes the images without changing their look or visual quality.

So, what makes the good news good?
First, Smush.it offers an API. and then, i finally found this plugin, WP Smush.it!

WP Smush.it seamlessly integrates Smush.it with WordPress. It automatically sends all the images you upload via the WordPress media uploader through the Smush.it API to optimize the images.

[tag] begin read [/tag]Yes. It performs images optimizations AUTOMATICALLY. Perfect.[tag] end read [/tag]