It doesn't exactly know — it just recognises objects and then asks for your reason to make it a business expense (it suggests a few options for each recognised

It doesn't exactly know — it just recognises objects and then asks for your reason to make it a business expense (it suggests a few options for each recognised object). Then you get an explanation of why this object can or can not be legally expensed. All of those options and explanations are pre-defined, so the whole app is more of an applied expression of what Tensorflow.js can do.