1. A method for object detection in an image plane, comprising the steps of: constructing a Hidden Markov Model (HMM) in an object detection system for an image, and initializing a plurality of HMM parameters; obtaining an object mask Ω(t) at current time through an object mask 106 h (t−1) at previous time using a parameter estimation unit in said object detection system, and updating said plurality of HMM parameters of current time on a spatial domain of said image; and re-estimating said object mask Ω(t) at current time based on the updated plurality of HMM parameters using a state estimation unit in said object detection system and a decoding algorithm in said state estimation unit.