That's exactly what I've read already, and it doesn't work, it's essentially an advanced guess, nothing more.
It is about chemistry and chemical substances, and it is simply not possible to analyze how potent these chemicals are using a digital camera.
Then it doesn't matter at all how many other pictures you compare with. It will always be a guess.
One thing that can be positive with that $72 gadget is that it can be a good complement, a good digital camera for taking close-up pictures of your buds.
But that's about it. To each his own...