1. An apparatus for reconstructing a panoramic X-ray image, the apparatus comprising: memory configured to store image data of multiple image layers detected by and received from a predetermined X ray detector through a predetermined communication link; at least one processor configured to perform at least one of determining a reference image layer among the multiple image layers, finding blocks that correspond to at least one block designated in the reference image layer from other image layers, selecting a block having a higher frequency in a predetermined frequency band, as a clearest block, from the found blocks by comparing frequencies in the predetermined frequency band of image data of the found blocks, and reconstructing the reference image layer by replacing the designated block in the reference image layer with the selected block as the clearest block in any of the other image layers, if the selected block is not the same as the designated block in the reference image layer; a display unit configured to display a panoramic image of the reconstructed reference image layer and a user input unit configured to receive an input signal for designating locations and the number of the blocks.