1. A method, comprising: generating, by one or more computing devices, a set of inter-image homographies for an image sequence comprising a plurality of frames according to a two-dimensional (2D) plane in at least two of the frames, wherein said generating comprises: estimating an inter-image homography for an initial frame pair according to a subset of a plurality of point trajectories that traverse the initial frame pair, each point trajectory in the plurality of point trajectories tracking a feature across two or more of the frames; and estimating an inter-image homography at each of one or more subsequent frame pairs according to a subset of the point trajectories that traverse the respective frame pair; wherein the inter-image homography at each frame pair corresponds to the plane at the respective frame pair.