An apparatus and a method for measuring the depth of an object in a scene and a method for computing image defocus and blur status are provided. An image analysis unit receives a plurality of reference blurred images, analyzes the reference blurred images, produces reference grey-scale distribution data, where the reference blurred images corresponds to a plurality of reference depths, respectively. A blur comparison module produces a blur model according to the reference grey-scale distribution data and the corresponding reference depths. The image analysis unit receives a target blurred image, analyzes the target blurred image, and produces and transmits target grey-scale distribution data to the blur comparison module for comparing the target grey-scale distribution data according to the blur model, and producing depth information. Moreover, the present invention further produces the corresponding blur status data, used in defocus and blur computations, according to the defocused and blurred image.