1. A method for registering three-dimensional (3D) CT image data with two-dimensional (2D) fluoroscopic image data using a plurality of markers, the method comprising: searching for a lateral angle and a cranial angle; moving a 3D mass center of a marker to a half segment between a source and a 2D mass center of the marker; computing a roll angle; computing a 3D translation coordinates; computing the roll angle and the 3D translation coordinates for a predetermined number of times successively; and overlaying the 3D CT image data on the 2D fluoroscopic image data based on the lateral angle, the cranial angle, the roll angle, and the 3D translation coordinates.