1. A method of obtaining a panoramic image, comprising steps of: a) positioning an object between an X-ray source exposing X-rays to a base image-layer-trace were regions of interest to be taken in the object and an image sensor receiving the X-rays having penetrated the base image-layer-trace; b) obtaining a frame image of a first region of the base image-layer-trace by exposing the X-rays to the first region, a start portion of the base image-layer-trace; c) obtaining frame images from a second region adjacent to the first region of the base huge-layer-trace to an n th region, an end portion of the base image-layer-trace, as the X-ray source and the image sensor move, wherein the frame images from the second region to the n th region are obtained by overlapping X-rays penetrating each region of the base image-layer-trace with the X-rays having penetrated previous region of the base image-layer-trace; c) obtaining panoramic images correspond to multiple image-layer-traces with use of the frame image of each region of the base image-layer-trace; d) dividing the multiple image-layer-traces into at least three regions respectively and determining at least two analysis regions; e) selecting an optimal image-layer-trace closely related to a focus-trace by analyzing the multiple image-layer-traces in the same analysis region; f) extracting a connecting-trace linking the optimal image-layer-traces selected in the regions; g) completing a final-trace by connecting the optimal image-layer-trace selected in each analysis region and the connecting-trace all together; and h) reconstructing a panoramic image corresponding to the final-trace.