1. A method for determining a three-dimensional movement of an object positioned on a table between an X-ray source and a digital image receiver in an imaging apparatus, wherein a plurality of radio-opaque markers are positioned on the object, the markers constituting a fixed reference frame and being within a single plane, the method comprising: taking, with the X-ray source, at least one first radiographic image of the markers for a first determined fixed position of the imaging apparatus in the fixed reference frame of the markers, the at least one first radiographic image of the markers forming a first plane (P 1 ); taking, with the X-ray source, at least one second radiographic image of the markers for a second determined fixed position of the imaging apparatus in the fixed reference frame of the markers, wherein the imaging apparatus has moved with respect to the first determined fixed position in the fixed reference frame of the markers, the at least one second radiographic image of the markers forming a second plane (P 2 ); calculating, with respect to the fixed reference frame of the markers, a planar homography with respect to a third plane between the first plane (P 1 ) and the second plane (P 2 ); determining a matrix (E 2 ) of extrinsic parameters of the imaging apparatus in the second determined fixed position by the calculating of the planar homography between the first plane (P 1 ) and the second plane (P 2 ); determining an inverse matrix (E 1 −1 ) of extrinsic parameters of the imaging apparatus in the first determined fixed position; and determining a matrix of the three-dimensional movement of the object with respect to the X-ray source of the imaging apparatus as a function of the inverse matrix (E 1 −1 ) of the extrinsic parameters of the imaging apparatus in the first determined fixed position and the matrix (E 2 ) of the extrinsic parameters of the imaging apparatus in the second determined fixed position.