ImageMagick - ImageMagick is a software suite to create, edit, and compose bitmap images.
PhotoPenguin App - PhotoPenguin is a completely free batch photo editor with support for cropping, resizing, adding watermarks, and converting photos to other formats. It works on the user's device, using the capabilities of modern browsers.
OpenCV - OpenCV is the world's biggest computer vision library
ImBatch - ImBatch is a batch image processor with a nice graphical user interface.
Cloudinary - Cloudinary is a cloud-based service for hosting videos and images designed specifically with the needs of web and mobile developers in mind.
Batch Image Resizer - Resize, crop, shrink, flip, exif-rotate, convert, enhance, process multiple pictures and photos with professional software! 120+ Actions, 30+ Image Formats