1. An image processing apparatus comprising: an input interface unit for receiving at least two projection images of a patient taken at different projection angles by an X-ray scanner, each of the images including a footprint of a target object, an image depth resolver configured to use the two target object footprints to determine whether the target object was external to the subject when the images were taken, based on a binocular disparity between the target object footprints; an image manipulator configured to, when the target object is determined by the resolver to be external, virtually replace or remove pixel information in the respective target object footprints to so produce an output enhanced image which, when viewed, no longer shows the target object footprints, and an output interface unit configured to output the output enhanced image.