Abstract: Based on geometrical facial features and thresholding,this paper presents a novel method for automatically locating human eyes in grayscale still images with complex background.A determination criterion of eye location is established by the priori knowledge of geometrical facial features.A range of threshold values that would separate eye blocks from others in a segmented facial image is estimated from the facial image histogram.With the progressive increase of the threshold by an appropriate step in that range,the size of existing blocks in the segmented facial image will expand,some existing blocks will merge into one block,and some new blocks will emerge.Once two eye blocks appear from the segmented image,they will be detected by the determination criterion of eye location.A 2-D correlation coefficient is used as a symmetry similarity measure to check the truth of detected eyes.