With Image Optimizer you can optimize every images on your site. It will scan the whole site, and pick up every image from themes, plugins and upload folder.
The default quality is 100%, which provides lossless optimization for JPEG and PNG images.
You can select images individually, and run batch optimization. Default image quality can be specified in plugin settings, however you can overwrite it before starting the optimization on selected images.
You can keep original images, so you can compare the optimized and the original image. This can be use to revert the optimization, if the optimized image quality doesn’t fit your needs, or if you want to re-optimize them with better quality. You can also remove original images afterward if you don’t need them anymore.