1. A position and orientation measuring apparatus comprising: a storage unit adapted to store character region specifying information and position information in association with a character region placed in a physical space; a detection unit adapted to detect the character region from first captured image data obtained by capturing an image of the physical space by an image sensing apparatus, using the character region specifying information stored in said storage unit; and an estimation unit adapted to estimate a position and orientation of the image sensing apparatus upon capturing the captured image data based on image position information of the character region, detected by said detection unit, in the first captured image data, and the position information which is stored in said storage unit and corresponds to the detected region.