code: def add_single_bd(
      x: np.ndarray, distance: int = 2, pixel_value: int = 1
  ) -> np.ndarray:
      """
      Augments a matrix by setting value some `distance` away from the bottom-right edge to 1. Works for a single image
      or a batch of images.
  
      :param x: A single image or batch of images of shape NWHC, NHW, or HC. Pixels will be added to all channels.
      :param distance: Distance from bottom-right walls.
      :param pixel_value: Value used to replace the entries of the image matrix.
      :return: Backdoored image.
      """
      x = np.copy(x)
      shape = x.shape
      if len(shape) == 4:
          height, width = x.shape[1:3]
          x[:, height - distance, width - distance, :] = pixel_value
      elif len(shape) == 3:
          height, width = x.shape[1:]
          x[:, height - distance, width - distance] = pixel_value
      elif len(shape) == 2:
          height, width = x.shape
          x[height - distance, width - distance] = pixel_value
      else:
          raise ValueError(f"Invalid array shape: {shape}")
      return x
  
imports: from typing import Optional, Tuple
  import numpy
label_desc: Use image node_id 1 for calling a global function with example usage: add_single_bd(x, distance, pixel_value) and returns: x