1. An image conversion apparatus comprising: a three-dimensional (3D) conversion instruction module configured to instruct execution of a 3D conversion required to convert an input image into a 3D image; a determination module configured to determine validity or invalidity of the 3D conversion instruction based on a type of the input image; and a converter configured to convert, based on validity determination of the 3D conversion instruction, the input image into the 3D image in response to the 3D conversion instruction, wherein the determination module is configured to determine invalidity of the 3D conversion instruction when the determination module determines that the input image corresponds to a 2D-converted image which has been converted from the 3D image into a 2D image.