1. A digital image composition method, adapted to eliminate a ghost image produced by a digital image-capturing apparatus due to handshakes in shooting, the method comprising: capturing a base image and a comparison image; selecting a base pixel from the base image, and setting a core window with the base pixel at the center; finding out a comparison pixel at a corresponding position from the comparison image according to an image position of the base pixel, and setting a search window with the comparison pixel at the center; comparing pixels in the core window one by one with pixels in a plurality of areas, wherein a center pixel of each of the areas is inside the search window, and a color pixel arrangement of each of the areas is identical to a color pixel arrangement of the core window; generating an absolute error sum value corresponding to each of the areas; looking up a primary region difference lookup table with a brightness value of the base pixel to find out a primary region difference value; subtracting the minimum absolute error sum value from the primary region difference value to get a normalized region difference value; determining whether the normalized region difference value is larger than a threshold value; increasing the brightness of the base pixel, if the normalized region difference value is larger than a threshold value; adding the brightness value of the base pixel to a brightness value of the comparison pixel corresponding to the minimum absolute error sum value, if the normalized region difference value is smaller than a threshold value; and completing all the pixels in the base image, and combining the modified pixels into a composed image according to positions thereof.