1. In an image processing method for inserting a given pattern at a target region having a particular location with respect to a scene being viewed by an image sensor which produces a series of successive image frames, wherein said scene includes at least two landmark regions displaced in position from one another; and wherein said method comprises the computation steps of (a) inferring the size and position of said particular location within each image frame of said scene from the size and position of a first one of said landmark regions represented within each image frame of said scene and (b) independently inferring the size and position of said particular location within each image frame of said scene from the size and position of a second one of said landmark regions represented within each image frame of said scene, whereby there may be a difference in the size and position of said particular location within each image frame of said scene inferred from the size and position of said second one of said landmark regions with respect to the size and position of said particular location within each image frame of said scene inferred from the size and position of said first one of said landmark regions; the improvement comprising the step of: c) modifying the size and position of the particular location within one of said image frames of said scene inferred from the size and position of said second one of said landmark regions within that one of said image frames so that it is substantially the same as the size and position of the particular location within that one of said image frames of said scene inferred from the size and position of said first one of said landmark regions.