1. A method of segmenting in a processor image data having a plurality of feature values at each pixel in a sequence of pictures, the feature values including pixel values and motion vector values, comprising: representing the data as points in a segmentation vector space which is the product of a vector space of feature values and a vector space of pixel addresses, representing segments as locations in the segmentation vector space, calculating a displaced frame difference by applying a motion vector from the segment to the pixel, and determining, using said processor, the membership of a segment for each pixel by a distance measured in segmentation vector space from the data point representing the pixel to the location of the segment, said distance in segmentation vector space comprising the components of: differences in pixel values between the pixel and the segment, differences in motion vector values between the pixel and the segment, and a displaced frame difference calculated by applying a motion vector from the segment to the pixel.