edit: Check out the list here https://github.com/quozd/awesome-dotnet/blob/master/README.md#image-processing:
- ImageResizer - Add commands to image URLs to get altered versions in milliseconds. Resizing, editing etc of images in real-time.
- ImageProcessor - Open-source .NET library to manipulate images on-the-fly.
- DynamicImage - High-performance open-source image manipulation library for ASP.NET.
- MetadataExtractor - Extracts Exif, IPTC, XMP, ICC and other metadata from image files.
- Emgu CV - Cross-platform .NET wrapper for the OpenCV library.
- DotImaging - Minimalistic .NET imaging portable platform
- Magick.NET - .NET wrapper for the ImageMagick library.
- OpenCvSharp - Cross platform wrapper of OpenCV for .NET Framework.
Check the AForge library. It is a set of libraries in which you'll find an image processing and a vision library.
