Markov random fields; Nonparametric Bayesian methods; Dirichlet process mixtures; Image segmentation; Clustering; Spatial statistics; Markov chain Monte Carlo, Image segmentation, Classification and discrimination; cluster analysis (statistical aspects), Spatial statistics, Random fields; image analysis, Computing methodologies for image processing, Dirichlet process mixtures, Clustering, spatial statistics, Markov chain Monte Carlo, Markov random fields, Image analysis in multivariate analysis, Nonparametric Bayesian methods, nonparametric Bayesian methods, image segmentation, Directional data; spatial statistics, clustering