1. An image detecting method, for determining a sequence of left-eye and right-eye image frames of an image signal, comprising: (a) performing block matching on a target area corresponding to two consecutive image frames of the image signal to determine a motion vector; (b) determining a current image frame from the two consecutive image frames as a left-eye image or a right-eye image according to the motion vector; (c) generating a stereo glass control signal according to a synchronous signal of the image signal and a result of the left-eye/right-eye image determination in (b); (d) respectively performing the step (a) and step (b) on a plurality of areas corresponding to the two consecutive image frames to generate a first plurality of determination results; and (e) compiling statistics of the first plurality of the determination results of the current image frame to determine the current image frame as a left-eye image or a right-eye image, wherein step (e) comprises increasing a first count value for each of the first plurality of determination results which indicates the left-eye image.