Maybe you could try to recognize different kinds of food, but I doubt that you could measure the volume of food by just one picture. Even humans would not be able to correctly guess the calories because there is not visual difference between low-fat cheese and regular cheese, for example.<p>You could also devise a "pregnancy test" app - simply take a picture of the woman's face - yes, of her face ;-) - and you get the result: pregnant or not, and whether it's a boy or a girl, and the due date. Honestly, people falling for the mealsnap app would also fall for this.
I can see this being a dangerous tool for people already kidding themselves about how many calories are in their food.<p>Eg:"That sign says this donut is 350 calories, but this app says it's only 100 if I take a picture of it from this angle"