1. A method for updating a 2D/3D registration between a three-dimensional image data set corresponding to a target area and a plurality of two-dimensional projection images of the target area, the target area being subjected to a movement, the method comprising: capturing, using an X-ray unit, the plurality of two-dimensional projection images of the target area; selecting, by a selection unit of a computing device, a plurality of contour points along a contour associated with a rigid object in the target area, the contour being visible in a first captured projection image and a three-dimensional image data set registered therewith; determining, by a displacement detection unit of the computing device, a displacement of each contour point of the plurality of contour points between the first captured projection image and a successively captured second projection image; obtaining, by a movement information detection unit of the computing device, movement information for each contour point of the plurality of contour points based on the determined displacement, the movement information describing a movement of the rigid object, wherein the obtaining comprises (1) restricting degrees of freedom of movement to observable movements that are perpendicular to a course of the contour in the three-dimensional image data set, and (2) solving a system of equations for a three-dimensional target plane that comprises the displaced contour point; forming a normal vector of the three-dimensional target plane, wherein the normal vector comprises a cross product of a first vector and a summation vector, wherein the first vector is formed as a cross product of a contour vector that stands perpendicular to the course of the contour in the three-dimensional image data set with a second vector that describes a three-dimensional position of a contour point prior to the movement, and wherein the summation vector comprises the contour point prior to movement on an image plane and a third vector describing a displacement in the image plane; and updating, by a registration-updating unit of the computing device, the registration based on the obtained movement information.