Abstract: On studying distribution of fogdrops made by fog machine, computer can be used to analyze the images of fogdrop micrograph and obtain statistical data. Due to the optical effects, such images tend to have brighter center and darker edge, thus affecting the accuracy of statistical results. To eliminate the uneven brightness, the authors used the method of taper brightness factor to process the images. The authors applied this method in their program to deal with the micrograph of fogdrops from fog machine experiment, and obtained a uniform average brightness of image processing and accurate results. This method can also be applied to correct similar uneven brightness of center and edge in the micrograph caused by optical effects.