OpenCV

OpenCV is a cross-platform, open-source library designed for use in real-time computer vision and image processing functions. It was originally developed by Intel, later by Willow Garage, and now maintained by Itseez. It is licensed under the free-to-use BSD license.

OpenCV is hardware-accelerated on most platforms, taking advantage of a computer's GPU to process images and videos very fast. It is developed in C++, but wrappers for C#, Ruby, Python, and Perl also exist.