1. An information processing method comprising: an image sensing step of acquiring sensed image data by sensing physical space by an image sensing unit; an orientation acquiring step of acquiring orientation information of the image sensing unit with an orientation acquiring unit; an index detecting step of detecting an index from the sensed image data with an index detection unit; a first calculation step of calculating a first reliability of the detection result based on the image data of the detected index in the sensed image data, without using the orientation information, with a first reliability calculation unit; a second calculation step of calculating a second reliability of the detection result based on predetermined index information, the orientation information, and the image data of the detected index in the sensed image data, with a second reliability calculation unit; and a determination step of determining, if the first reliability is high, that the detected index is an index included in the sensed image data, and if the first reliability is not high and the second reliability is low, that the detected index is not an index included in the sensed image data.