1. A display apparatus, comprising: a processor to control one or more processor-executable units; a visual fatigue estimating unit to estimate a degree of visual fatigue corresponding to an input 3-dimensional (3D) image, wherein the visual fatigue estimating unit comprises: a motion vector calculating unit to calculate a motion vector corresponding to the input 3D image; and a visual fatigue determining unit to estimate the degree of visual fatigue using the motion vector calculated by the motion vector calculating unit; and an image adjusting unit to rescale a depth level of the input 3D image based on the degree of visual fatigue.