ImageProcessor
Wrapper around System.Drawing for the processing of image files
...It’s lighting fast, extensible, easy to use, comes bundled with some great features and is fully open source. ImageProcessor is free and open source but developing it has taken thousands of hours of my time and a large part of my sanity. If you feel like dropping me a few precious pounds (there’s no obligation) it would go a great way to ensure that I can afford to take the time to continue to improve the library. It's fast, extensible, easy to use, comes bundled with some great features and is fully open source.