Funny, I was just discussing this on HN a few days ago:

https://news.ycombinator.com/item?id=44185892

There's a lot of questions about the nutritional content of food which you can't answer just by looking at a photo, like "is that a glass of whole milk or non-fat", or "are those vegetables glossy because they're damp or because they're covered in butter". No amount of AI magic is going to solve that.