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This paper describes a video surveillance system capable of recognizing human postures from video sequences. The system comprises of two key modules: human detection and posture classification. In the module of human detection, human blobs are extracted by the technique of background subtraction. An adaptive background model is employed to characterize the dynamics and complexity of outdoor scenes based on the mixture of Gaussians. In order to formulate the variations of human postures, pseudo 2D hidden Markov models (P2DHMM) is employed for representing and recognizing human postures based on its '2-D elastic matching' property. It is trained to differentiate human postures and tolerate the variations of the same human posture using embedded Viterbi and segmental K means algorithms. In the classification of human postures, observation sequence is extracted from current image frame. The probabilities of observation sequence corresponding to each P2DHMM model are computed by doubly embedded Viterbi optimization, and human blob is classified as the human posture with the highest likelihood.