1. A method of segmenting an object in a set of image data using one or more prior instances of the object, comprising: determining a nonparametric estimate of a property from the one or more prior instances of the object in a subspace spanned by the one or more prior instances of the object; imposing the nonparametric estimate of the one or more priors in a Bayesian expression conditioned on the set of image data; and selecting a segmentation of the object in the set of image data by executing a level set method which optimizes the Bayesian expression.