1. An image registration method for registering a target image with a reference image, comprising: determining a target set of features present in the target image; determining a reference set of features present in the reference image; generating respective signatures for each feature in the target and reference sets; matching features from the target set to corresponding features in the reference set using the signatures; generating respective transformations to map pairs of features in the target set to corresponding pairs of features in the reference set; and determining a global transformation for the target image using a measure of the accuracy of the transformations.