ImageMagick - ImageMagick is a software suite to create, edit, and compose bitmap images.
imgix - Real-time Image Processing. Resize, crop, and process images on the fly, simply by changing their URLs.
OpenCV - OpenCV is the world's biggest computer vision library
Cloudimage - Cloudimage.io is the easiest way to resize, store, and deliver your images to your customers through a rocket fast CDN.
FFmpeg - Open source multimedia suite for conversion, playback, profiling, and streaming.
Sirv - Dynamic image processing, hosting and rich-media for retailers and eCommerce.