An object-based analysis-synthesis coder for coding moving images at low data rates is investigated. The coder is based on the source model of articulated 3D objects. This model describes the real objects by means of model objects define by shape, motion and color parameters. The model objects may be articulated, i.e. they consist of several rigid object components linked to each other by joints. In this contribution a new algorithm for joint position estimation is presented. First the motion parameters of the connected object components are estimated at different times. For motion estimation a Maximum-Likelihood estimator is applied. Then the position of the joints is determined by evaluating the estimated motion parameters in the equations representing the constraints imposed for the joints on the relative motion of the connected object components. The algorithm was applied to a synthetic test sequence (CIF, 10 Hz). At a camera noise figure of 40 dB a joint position estimation average error of 0.94 pel can be achieved.