1. An index identification method for detecting and identifying an index from an acquired image using position information and geometric information of the index, which are held in advance, comprising: an image acquisition step of acquiring an image obtained by sensing a real space including an index having a predetermined shape by an image sensing device; a position and orientation information acquisition step of acquiring measurement results of a three-dimensional position and orientation of at least one of the image sensing device and the real object; and an index identification step of detecting and identifying the index from the acquired image on the basis of the three-dimensional position and orientation measurement results, and the position information and the geometric information of the index.