Ashampoo® Photo Optimizer - Ashampoo Photo Optimizer 8 enhances your photos at the click of a button! The program fully automatically adjusts colors, contrasts and exposure settings to perfection for individual images or entire collections.
ImageOptim - Faster web pages and apps.
TinyPNG - Make your website faster and save bandwidth. TinyPNG optimizes your PNG images by 50-80% while preserving full transparency!
jStrip - jStrip is a free tool to reduce the file size of JPEG images without sacrificing image quality.
iLoveIMG - iLoveIMG is one of most powerful solution that comes with all the major tool you cloud want to edit images in bulk.
ImageAlpha - ImageAlpha is a GUI for pngnq and pngquant.