Center-determination of laser spot is key to crown placement measurement system because it immediately concerns accuracy of the displacement. By using Matlab software, the grabbed laser spot image was smoothed with noise cancellation and median filtering to improve separating capacity of the targets and background, which set the terms for the object extraction. Then the image was segmented with Canny operator to extract target image from cluttered background. Finally, based on the extracted target, center coordinates of the laser spot can be found by using gray barycenter algorithm.