1. A calibration method for calibrating an optical touch display, wherein the optical touch display comprises a plurality of image detecting sensors, the calibration method comprising the following steps: generating a plurality of calibration points; generating a plurality of representative calibration points from the plurality of calibration points; obtaining a first image position of each representative calibration point relative to the plurality of image detecting sensors via the plurality of image detecting sensors; constructing a coordinate transformation mechanism for transforming the first image position of each representative calibration point relative to the plurality of image detecting sensors to a first screen position of each representative calibration point relative to the optical touch display; calculating a relative position between each representative calibration point and its neighboring calibration points; calculating a second image position of each calibration point relative to the plurality of the image detecting sensors based on the relative position and the first image position; and calculating a second screen position of each calibration point relative to the optical touch display via the coordinate transformation mechanism and the second image position.