code: def pngValidator(path=None, data=None, fileObj=None):
      """
      Version 3+.
  
      This checks the signature of the image data.
      """
      assert path is not None or data is not None or fileObj is not None
      if path is not None:
          with open(path, "rb") as f:
              signature = f.read(8)
      elif data is not None:
          signature = data[:8]
      elif fileObj is not None:
          pos = fileObj.tell()
          signature = fileObj.read(8)
          fileObj.seek(pos)
      if signature != pngSignature:
          return False, "Image does not begin with the PNG signature."
      return True, None
  
imports: import calendar
  from io import open
  import fs.base
  import fs.osfs
  from collections.abc import Mapping
  from fontTools.ufoLib.utils import numberTypes
label_desc: Use image node_id 41 for calling a global function with example usage: pngValidator(path, data, fileObj) and returns: True,  None, False,  str