An image processing system (IPS), comprising an input interface (IN) for receiving a projection image from a plurality of projection images of a movable object (PAT) acquired along different directions by an imaging apparatus (XA), the projection images defined in a projection domain spanned by a radiation sensitive surface of the detector (D). The system includes a motion checker (MC) configured to operate in the projection domain to decide whether the projection image is corrupted by motion of the object during acquisition.