1. Within an image acquisition device, a method of cross-correlating integral projection vectors, comprising: acquiring a sequence of image frames; determining a measure of frame-to-frame rotation, including: determining horizontal and vertical integral projection vector gradients for each of a first frame and a second, following, image frame in said sequence; normalizing said integral projection vector gradients; determining locations of primary maximum and minimum peaks of said integral projection vector gradients, and based on normalized distances between the primary maximum and minimum peaks, determining a global image rotation; and performing a further action based on the determined global image rotation.