An electronic device is provided. The electronic device includes: an image sensor, a display device, and a processor. The image sensor captures a plurality of object images of a target object on which a first positioning tag, a second positioning tag, and a third positioning tag are disposed. The processor executes an augmented-reality program to perform the following steps: recognizing the first positioning tag, the second positioning tag, and the third positioning tag from each object image; calculating a scale ratio for each dimension of a three-dimensional model according to the positions of the first, second, and third positioning tags; performing an image-scaling process on the three-dimensional model and rendering the scaled three-dimensional model; and overlaying the scaled three-dimensional model on each object image to generate an output image and displaying the output image on the display device.