1. Method for repositioning a numerically controlled device, by using an image taken of the object as an aid, characterized in that the system is taught by defining a child image from the camera's image, by forming its own set of coordinates, or a set of co-ordinates retrieved from elsewhere, and recording the image thus obtained, together with its co-ordinates in the data system, and, in the repositioning situation, comparing the real-time image with the child image stored in the data system, in order to determine the real-time position of the imaging device relative to the stored image.