1. A method for designing an image restoration filter of an imaging system, comprising: obtaining first image information of a test image, wherein the first image information comprises pixel values of a plurality of pixels in the test image and the test image comprises at least one reference mark; obtaining second image information by capturing the test image from an image sensor of the imaging system; detecting position information of each reference mark in the second image information through an image recognition technique; performing an image correction process to the second image information according to the position information of the reference mark; and obtaining the image restoration filter according to the first image information and the second image information through a numerical method such that the second image information after being processed by the image restoration filter has a better similarity to the first image information.