A method for filtering image noise includes the steps of: acquiring an image; converting gray-scale values of the image and sharpening the image; defining axes perpendicular to image borders and selecting intersecting points between the axes and the image border; creating an object points set and inputting all the intersecting points into the object points set; fitting a geometric character according to the object points set; defining a tolerance threshold value; selecting an intersecting point from the object points set; calculating a distance from the selected intersecting point to the geometric character; determining whether the distance is larger than the defined tolerance threshold value; marking the selected intersecting point as a noise if the distance is larger than the defined tolerance threshold value; and deleting the selected intersecting point from the object points set. A related method is also disclosed.