What are some alternatives?
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!
JPEGmini - JPEGmini - The Photo Optimization Tool Trusted by Tens of Thousands Image Perfectionists
WP Smush - Reduce image file sizes, improve performance and boost your SEO using the free WPMU DEV WordPress...
Optimus.io - Lossless image optimization
ON1 Resize - High quality photo enlargement up to 1000%.