1. A method for calibrating image deformation, adapted to an image capturing device having a first lens, a second lens, a focusing actuator, and a pre-stored first focusing step-to-focusing distance ratio, comprising: capturing a plurality of image sets by utilizing the first lens and the second lens, wherein each of the image sets comprises a first image corresponding to the first lens and a second image corresponding to the second lens, and the image sets comprise a reference image set including a first reference image corresponding to the first lens and a second reference image corresponding to the second lens; detecting whether the reference image set is deformed and detecting a focusing condition of the image capturing device; when the reference image set is detected to be deformed and when the focusing condition of the image capturing device is a far focusing condition: recording a focusing step corresponding to a focused target in each of the image set, wherein the focusing step corresponding to the focused target in each of the image sets is a number of steps that the focusing actuator is required to move the first lens and the second lens to a focusing position for generating each of the image sets; when the focusing step corresponding to the focused target in each of the image sets reaches a convergent value, obtaining a minimum focusing step and calculating a difference value between the minimum focusing step and the convergent value; and calibrating the first focusing step to focusing distance ratio according to the difference value; and when the reference image set is detected to be defored and when the focusing condition of the image capturing device is a near focusing condition: performing a three-dimensional depth estimation on each of the image sets to generate depth information of the focused target in each of the image sets; obtaining the focusing distance corresponding to the focused target in each of the image sets according to each of the depth information; performing a regression according to the focusing distance and the focusing step corresponding to the focused target in each of the image sets; and calibrating the first focusing step-to-focusing distance ratio according to a result of the regression.