code: def check_image_file_header(filename):
    
    with tf.gfile.Open(filename, 'rb') as f:
      magic = read32(f)
      read32(f)  # num_images, unused
      rows = read32(f)
      cols = read32(f)
      if magic != 2051:
        raise ValueError('Invalid magic number %d in MNIST file %s' % (magic,
                                                                       f.name))
      if rows != 28 or cols != 28:
        raise ValueError(
            'Invalid MNIST file %s: Expected 28x28 images, found %dx%d' %
            (f.name, rows, cols))
docs: Validate that filename corresponds to images for the MNIST dataset.