how to track object motion with webcam

I had assigned a project that track player hand to control game object (such as dog , fish) to move. Therefore, I need someone can provide some way to help me finish the project. I need some tutorial to use webcamtexture and how to track hand. I had search OpenCV that it may help me to finish the project, but i do not know how to apply it to Unity. Although I saw OpenCVforUnity in Asset Store, but I cannot afford the charge (since no budget). Is there are any free api to have me to track hand? If no, how can i code to track hand?

sorry for poor English