Wordpress Plugin Review: Optimus Image Compressor

 
Images often account for most of the downloaded bytes on a web page and also often occupy a significant amount of visual space.
As a result, optimizing images can often yield some of the largest byte savings and performance improvements for your website: the fewer bytes the browser has to download, the less competition there is for the client's bandwidth and the faster the browser can download and render useful content on the screen. Optimized images will speed up website and improve rank.  Google likes optimized websites.

There are many wordpress plugins and API available for lossless image optimization. Some of them are very good in quality and Optimus is one of the best.
Wordpress Plugin Review: Optimus Image Compressor