We have proposed a mixed reality based painting system. In this paper, we tackle a problem in our previous painting system that fully relies on magnetic sensor that is attached on the canvas, the users needed to detach and attach a sensor on the canvas during painting when they want to switch the canvas. Instead of that, in this paper, we aim to automatically detect the shape of the canvas for registration purpose. Using the shape or region detection method such as MSER (maximally stable extremal regions), we detect and track the shape on the canvas on the captured camera image. We then compute the camera pose for virtually overlay the painting result. Using the brush device, we can draw and paint freely on the tracked canvases. We show that using visual based tracking method, we can generate the equivalent result compared to the result of using the sensor.