In this paper we introduce a commercial interactive whiteboard (IWB) system named ImSensorTouch by ImSensor Inc. Using this interface system, we can control our computer through the interactive whiteboard screen just by touching it with your finger or a pen. The interface interacts with Windows operating system (OS) and is adaptable to changes of surroundings especially temperature, and illumination condition. The proposed system calculates the difference between a reference image and a current image captured by a camera in the optical receptive field. And the position making the difference is used to generate the position on Windows screen. Then, we send a mouse event on the position to Windows OS. We have implemented the system using a critical section(CS) with two threads for the reference frame update process in which an adaptive thresholding technique is periodically exploited to get reliable result. We expect the system is competitive and promises a bright future in the IWB market.