ImageMagick - ImageMagick is a software suite to create, edit, and compose bitmap images.
OpenCV - OpenCV is the world's biggest computer vision library
Cloudinary - Cloudinary is a cloud-based service for hosting videos and images designed specifically with the needs of web and mobile developers in mind.
imgix - Real-time Image Processing. Resize, crop, and process images on the fly, simply by changing their URLs.
XnConvert - XnConvert is an easy image converter for graphic files, photos and images available on Windows...
Scikit Image - scikit-image is a collection of algorithms for image processing.