1. An image processing system comprising a camera, an image processor and a calibration surface, the calibration surface including thereon a calibration pattern, the calibration pattern comprising a plurality of alternately coloured elements which provide a corresponding plurality of corners at locations on the calibration pattern at which more than two of the coloured elements adjoin, the corner locations defining a first group of lines and a second group of lines, the lines in each of the group of lines being parallel with respect to each other on calibration surface, the first group of lines being orthogonal to the second group of lines, the camera being operable to generate a video signal representative of a scene as viewed by the camera, the scene including the calibration surface, the image processor being operable to detect from the video signal at least some of the corner locations to identify the first and second group of lines of the calibration pattern, to extrapolate the lines from each group of lines to determine a presence and a location of a first intersection point on a plane of the scene as viewed by the camera at which the extrapolated lines from the first group intersect and a second intersection point on the plane of scene as viewed by the camera at which the extrapolated lines from the second group intersect, and to estimate from the presence and the location of the first and second intersection points one or more of an estimated roll angle value, an estimated pitch angle value and an estimated yaw angle value corresponding to a roll angle, pitch angle and yaw angle of the camera relative to the calibration surface, wherein the detection of the corner locations by the image processor comprises identifying from the video signal a plurality of potential corner locations, defining an area of the scene as viewed by the camera centred around each potential corner location, analysing a colour of points lying on a periphery of each area, to estimate a likelihood that a corner is located at each potential corner location.