1. An image processing method for an image processing device, the image processing device storing a coordinate of a feature point and data of a first straight line of a first image, and the data of the first straight line comprising a coordinate of a first straight line starting point and a coordinate of a first straight line finishing point, the image processing method comprising: (a) the image processing device calculating a first distance between the coordinate of the first straight line starting point and the coordinate of the feature point; (b) the image processing device calculating a first weight of the coordinate of the first straight line starting point relative to the coordinate of the feature point according to the first distance, wherein the first distance is reversely related to the first weight; (c) the image processing device calculating a coordinate of a second straight line starting point in a second image relative to the coordinate of the first straight line starting point according to the first weight; (d) the image processing device calculating a second distance between the coordinate of the first straight line finishing point and the coordinate of the feature point; (e) the image processing device calculating a second weight of the coordinate of the first straight line finishing point relative to the coordinate of the feature point according to the second distance, wherein the second distance is reversely related to the second weight; and (f) the image processing device calculating a coordinate of a second straight line finishing point in the second image relative to the coordinate of the first straight line finishing point according to the second weight.