1. A computer-implemented method of estimating, using a processor, a transformation between a first image and a second image, comprising: extracting a plurality of interest points in the first image; defining a region of the first image around each of said extracted plurality of interest points in the first image; computing a local descriptor for each region of the first image; extracting a plurality of interest points in the second image; defining a region of the second image around each of said extracted plurality of interest points in the second image; computing a local descriptor for each region of the second image; using an area-based similarity measure and the computed local descriptors to estimate parameters of a local transformation between each region of the first image and each region of the second image, to derive a plurality of estimated local transformation parameters associated with respective pairs of interest points from the first image and the second image, wherein the similarity measure is invariant to rotation and scale; identifying a cluster of estimated local transformation parameters in the set of estimated local transformation parameters; determining pairs of interest points from the first image and the second image that are associated with the estimated local transformation parameters in the identified cluster; and providing the determined pairs of interest points for use in a robust estimator to derive a global transformation between the first image and the second image, wherein at least one of the above steps is performed by said processor.