I saw a demo awhile back of an app that would try to estimate calories based on pictures of food. It was wildly inaccurate. For people who are determined to make it work, counting calories requires an obsessive mindset that will weigh a handful of nuts before eating them.

This is one of the few use cases where Soylent ( the pseudo food ) may be superior. Because you can guarantee that you are eating x calories per day and only x calories per day.

But then, you'd be living on soylent...