What are some alternatives?
imgix - Real-time Image Processing. Resize, crop, and process images on the fly, simply by changing their URLs.
Crunch - Crunch is an OS X tool for PNG image file optimization.
Cloudinary - Cloudinary is a cloud-based service for hosting videos and images designed specifically with the needs of web and mobile developers in mind.
ImageKit.io - Instant multi-platform image optimization
ImageOptim - Faster web pages and apps.
Smaller - Make your websites load faster