1. An apparatus for obtaining depth information using an optical pattern, the apparatus comprising: a pattern projector to generate the optical pattern using a light source and an optical pattern projection element (OPPE), and to project the optical pattern towards an object area, the OPPE comprising a pattern that includes a plurality of pattern descriptors; an image obtaining unit to obtain an input image by photographing the object area; and a depth information obtaining unit to measure a change in a position of at least one of the plurality of pattern descriptors in the input image, and to obtain depth information of the input image based on the change in the position, wherein the pattern of the OPPE is adapted to obtain the depth information, wherein the OPPE is configured to accurately focus shapes of the pattern of the OPPE on the object area by projecting on a space, and wherein the depth information obtaining unit obtains depth information of the input image according to Equation 1: z ⁡ ( x i , y i ) = g ⁡ ( x i , y i , x p , y p , ) + w z = D 2 ⁢ ( x p ⁢ tan ⁡ ( θ p 2 ) - x i ⁢ tan ⁡ ( θ i 2 ) ) + tan ⁡ ( θ i 2 ) - tan ⁡ ( θ p 2 ) + w z [ Equation ⁢ ⁢ 1 ] where z (x i , y i ) denotes a depth value of a pattern descriptor having coordinates (x i , y i ) in the input image, (x p , y p ) denotes coordinates of the optical pattern, θ p denotes a projection angle of the pattern projector, θ i denotes an incidence angle of the image obtaining unit, D denotes a center distance between the pattern projector and the image obtaining unit, and w z denotes a distortion correction item between a pattern included in the optical pattern and a pattern included in the input image.