The accuracy of automatically aligned sub-images in a stitched X-ray image is assessed by obtaining displacement vectors of two sub-images that are aligned by an auto alignment method and another method where the alignment is determined by position sensor feedback from an X-ray source that is moved in relation to the imaged object. An error value associated with the displacement vectors of the auto alignment sub-images and the relative motion alignment sub-images is determined and compared to a Gaussian error distribution model to give a registration level indicating the relative alignment accuracy of the auto aligned sub-images. The registration level may be a sigma level of the Gaussian distribution model.
