1. A method comprising: computing an initial alpha matte from an input image; and automatically updating the initial alpha matte, wherein automatically updating comprises: selecting one or more shape models from a shape model database, wherein the shape model database comprises a plurality of principal component analysis-based shape models trained using eigen analysis; incorporating the one or more shape models into the initial alpha matte; incorporating one or more alignment parameters into the initial alpha matte to align the one or more shape models in the initial alpha matte; and optimizing the initial alpha matte to obtain an optimized alpha matte, wherein optimizing the initial alpha matte to obtain the optimized alpha matte comprises iteratively solving a quadratic cost function to determine the one or more alignment parameters that produce a minimum value of the quadratic cost function.