使用opencv计算到红点的距离

i'm newbie with opencv. Just managed to install and set it up to Visual 2013. I tested it with a sample of live stream for my laptop's camera and it works. Now i want to calculate the distance with the webcam to a red laser spot that will be in the middle of the screen(live_stream). Tell me from where can i start? I know that i must find the R(red) pixel from the middle of the screen but i dont know how to do that and what functions can i use. Some help, please? The live stream from webcam that works is shown below:i'm newbie with opencv. Just managed to install