1. A computer-implemented method of annotating images in a data set comprising a first set of images which initially have annotations and a second set of images which initially do not have annotations, the method comprising: determining spatial correspondences for all pairs of images in the data set, wherein each spatial correspondence represents a mapping of a location in a first image in the first set of images to a corresponding location in a second image in the second set of images; for each mapping, calculating a connection strength between the location in the first image and the corresponding location in the second image; and iteratively propagating information across images in the data set using the connection strengths of the mappings as weights for propagating the information, augmented by an estimate of propagation accuracy, wherein the propagated information is used to provide annotations to images which do not initially have annotations, and wherein each iteration performs a propagation across all images in the data set.