code: def mask_img():
      mask = np.ones(SHAPE)
      mask[:5] = 0
      mask[-5:] = 0
      mask[:, :5] = 0
      mask[:, -5:] = 0
      mask[..., -2:] = 0
      mask[..., :2] = 0
      return Nifti1Image(mask, _affine_eye())
  
imports: import numpy
  import pytest
  from nibabel import Nifti1Image
  from numpy.testing import assert_array_almost_equal
  from nilearn._utils.testing import write_imgs_to_path
  from nilearn.conftest import _affine_eye, _rng
  from nilearn.decomposition.canica import CanICA
  from nilearn.image import get_data, iter_img
  from nilearn.maskers import MultiNiftiMasker
label_desc: Use image node_id 4 for calling a global function with example usage: mask_img() and returns: Nifti1Image