1. A method for determining a registration vector between two selected images of a group of at least three related images, the method comprising; a. determining a set of registration vectors, each being between a respective pair of images in the group; b. determining, from the set of registration vectors, at least one composite registration vector leading from one selected image to the other selected image via at least one image other than the selected images; c. determining an optimized registration vector, being the average of a plurality of registration vectors selected from; i. the registration vector between the selected images ii. the at least one composite registration vector.