1. A video image stabilisation system for correction of camera motion, that is arranged to receive one or more signals representative of a plurality of images from an image source wherein, for an image n following at least an image (n−1) and an image (n−2) the system is arranged to estimate a Global Motion Offset (GMO) value between image n and a previous image representative of the spatial separation between the scene imaged in image n and the previous image, and apply a corrective movement to the image n based upon this GMO, characterised in that: the system is arranged to estimate the GMO for the image n with reference to a mask that represents a region or regions of the image n not to be considered in the GMO estimation, the region(s) being region(s) estimated as likely to mislead the estimation of the GMO and wherein the system is arranged to examine one or more local regions of the image n and corresponding local regions of a previous image, and estimate a local motion offset (LMO) representative of spatial separation between like features in corresponding local regions of the current and previous images, and if the, or each, LMO is greater than a given threshold, to set area(s) of the mask that correspond to this local region or regions to indicate omission from the GMO estimation, wherein the LMO values of those parts of the image not masked are not used in the calculation of the GMO.