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 relation, 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 when the reference image set is detected to be deformed, calibrating the first focusing step-to-focusing distance relation according to a focusing step and a focusing distance corresponding to a focus target in each of the image sets, wherein the focusing step corresponding to the focus target in each of the image sets is the 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.