An apparatus comprises: an image analyzer configured to analyze at least two images to determine at least one matched feature; a camera definer configured to determine at least two difference parameters between the at least two images; and a rectification determiner configured to determine values for the at least two difference parameters in an error search using an error criterion based on the at least one matched feature in the at least two images and an estimated difference parameter value, wherein the value for each difference parameter is determined serially.