[Plugin: CW Image Optimizer] no error messages but plugin doesn't optimize images

Hi, I’ve installed littleutils and plugin with no problems. I don’t have any error message, but all images say “no savings” after optimize them. I test them in Shushit.com and they had some kb to compress. So there is something wrong. I really would like to use this plugin. Any idea?

https://www.ads-software.com/extend/plugins/cw-image-optimizer/