1. An image depth recovering method using a stereo image fetching device, the method comprising: generating a plurality of 2D images respectively fetched by cameras disposed on the stereo image fetching device into a plurality of depth maps carrying information of depths on the plurality of 2D images; transforming the plurality of 2D images carrying respective depth maps into a plurality of pre-processed images; generating a plurality of rectified images by applying a rectification procedure to the plurality of pre-processed images to reduce effects of epi-polar lines caused by linear movements of an object in the plurality of 2D images; retrieving a first plurality of disparities between the plurality of rectified images, in a form of a DSI space which indicates a space defined by the displacement between two cameras when fetching two 2D images corresponding to two rectified images, a moving distance of the object between both the rectified images, and a Hamming distance between the two rectified images; calculating a disparity map that minimizes plain data disparity for indicating image consistency between images, and smoothness of images; and utilizing the disparity map to recover the image depth.