I'm skeptical
As someone who has lived with serious pain for many years, I've learned how to not show it because it makes conversation with other people more pleasant. They don't need to know. Actually, I think this is something that most people do naturally to some extent. For example, when you ask someone how they are, they usually smile and say "great!", even if they are in pain. I can't remember the last time someone answered "miserable, and you?" Anyway, I doubt that facial expressions can be read by anything in order to decode things like this. Humans have always had a mask. We're built that way. In fact the word "persona" means "mask". Nevertheless, it would be hard for even a ouja board to do worse than people at recognizing pain in others.