1. A system ( 100 ) for segmenting an object in image data using model-based image segmentation, the system comprising a feature unit ( 120 ) for identifying features in the image data for computing an external energy of a mesh on the basis of a current position of the mesh, wherein the feature unit ( 120 ) further comprises: a candidate feature unit ( 122 ) for selecting a plurality of candidate features in the image data, for identifying a feature to be included in the features identified in the image data; a position unit ( 124 ) for determining a position of each candidate feature of the plurality of the candidate features relative to a region of the image data; a feature function unit ( 126 ) for computing a strength of the each candidate feature, wherein the strength of the each candidate feature depends on the position of the each candidate feature relative to the region; and an evaluation unit ( 128 ) for evaluating the each candidate feature of the plurality of candidate features and for identifying the feature among the plurality of candidate features based on this evaluation.