1. A method for detecting motion pixels in image, comprising steps of: step 1: obtaining difference image between current image and background image; step 2: finding a binarization threshold from the distribution of all absolute pixel values in said difference image; step 3: using all or part of the pixel values, in said difference image, whose absolute values are smaller than or equal to said binarization threshold to compensate the effect of illumination change and to obtain an updated difference image; step 4: finding a binarization threshold from the distribution of all absolute pixel values in said updated difference image, changing the pixel values whose absolute values are larger than said binarization threshold to high, and changing the pixel values whose absolute values are equal to or smaller than said binarization threshold to low, thereby obtaining a binarized updated difference image; and step 5: determining pixels in said binarized updated difference image whose values are high as motion pixels.