Note: Newer versions of Processing are no longer compatible with this library. This OpenCV library works with the later versions of Processing, however, my code is not compatible with it. I'll try and update this Instructable when I get a chance.
First of all, you will need a computer that has Processing installed. Processing is free and open source, so download it and install it on your computer right now! It is a powerful tool and has a very active community of people working with it.
You will also need to install OpenCV and the Simple-OpenCV library for Processing. If you are using a Mac, you can follow this Instructable otherwise you can always follow the directions on this website.