docs: def generate_img_id(profile, ext=None, label=None, tmp=False):
      """
      Generates img_id.
      """
      if ext and not ext.startswith('.'):
          ext = '.' + ext
      if label:
          label = re.sub(r'[^a-z0-9_\-]', '', label, flags=re.I)
          label = re.sub(r'_+', '_', label)
          label = label[:60]
      return '{profile}:{tmp}{dtstr}_{rand}{label}{ext}'.format(
          profile=profile,
          tmp=(dju_settings.DJU_IMG_UPLOAD_TMP_PREFIX if tmp else ''),
          dtstr=datetime_to_dtstr(),
          rand=get_random_string(4, 'abcdefghijklmnopqrstuvwxyz0123456789'),
          label=(('_' + label) if label else ''),
          ext=(ext or ''),
      )