There's already a lot of calorie-counting apps out there if that's what somebody is interested in. dailyburn.com, for instance, is pretty good. It's also a lot of work to replicate one of these since you'll need to enter a huge database of possible foods.

The problem with them is that counting calories is too damn much work, so adding an extra step, where you take a photo of your food and then count the calories in it, doesn't seem like a huge gain. On the other hand, I suppose if you had photos of everything you'd eaten you could more easily count the calories only once every couple of days.

Still, I think you'll need to decide between "food porn" and "healthy eating" rather than try both, since they're pretty much opposed.