1. An image alignment method comprising: fetching at least two consecutive images from images captured from an object sequentially; calculating a relative displacement between said two consecutive images, wherein said relative displacement is a shift between any two consecutive images of said images which can be calculated by a phase correlation algorithm utilizing a filter G to pass low-frequency signals, and is estimated by the following equation: [ p ⁢ ⁢ 1 , p ⁢ ⁢ 2 ] shift ⁡ [ x , y ] = Max ⁢ { F - 1 ⁡ [ F ⁡ [ p ⁢ ⁢ 1 ] ⁢ ( F ⁡ [ p ⁢ ⁢ 2 ] ) *  F ⁡ [ p ⁢ ⁢ 1 ]  ⁢  F ⁡ [ p ⁢ ⁢ 2 ]  ] ⁢ G } where p 1 and p 2 are any two consecutive images of said images, F is a Fourier transfrom function, G is said filter, x denotes the x-coordinate of the maximum displacement of p 1 and p 2 , and y denotes the y-coordinate of the maximum displacement of p 1 and p 2 ; calculating an absolute displacement which is a shift between any one of said images and the first image of said images; and computing a common area of said images by utilizing said relative displacement and said absolute displacement, and deleting remainder portions of said images excluding said common area.