message: The PNG image type should be at offset 25 - not 27
  8 header
  8 IHDR start
  4(width) + 4(height) + 1 bit depth
  26th byte is color type
diff: @@ -198,7 +198,7 @@ static bool hasTransparencyPng(const std::string& data)
  if (data.compare(12, 4, "IHDR") != 0)
  return false;
  - int ctype = data[27];
  + int ctype = data[25];
  if (ctype != 3)
  return ctype == 4 || ctype == 6;
  