code: def create_square():
      square = np.zeros((256, 256, 3), dtype=np.int16)
      square[42:213, 42:213, :] = 1
      square[71:185, 71:185, :] = 2
      square[99:157, 99:157, :] = 3
  
      return square
  
file_path: dipy/dipy/segment/tests/test_mrf.py
imports: import numpy
  import numpy.testing
  from dipy.data import get_fnames
  from dipy.sims.voxel import add_noise
  from dipy.segment.mrf import ConstantObservationModel, IteratedConditionalModes
  from dipy.segment.tissue import TissueClassifierHMRF
  from dipy.testing.decorators import set_random_number_generator
label_desc: Use image node_id 2 for calling a global function with example usage: create_square() and returns: square