Interesting concept, although I don’t think taking a pic of what I am eating will help me — when I realize that most of the apps that estimate calories are wrong. There are so many factors that determine how many calories something is — for me, its more accurate to stick to whole, clean foods than to count calories. Eating paleo means I don’t watch calories – which is freedom.

In the fast-growing market for electronic exercise-and-diet diaries, the holy grail might be a camera that would deliver not only a photograph but also a calorie count. And fast.

How else to account for that bowl of Aunt Pam’s chicken-pot pie? The lobster-linguine entree at your favorite restaurant? Or any meal that doesn’t come from a label-bearing box?

Now purporting to deliver on that promise is a new app (for the iPhone, iPod touch and iPad running iOS 4.0 or higher) called Meal Snap. At $2.99, it comes closer to the mark than perhaps anything else on the market. But mostly it demonstrates the steepness of the challenge. In a WSJ test, only seven of of 17 meals photographed via an iPad camera and delivered to Meal Snap produced an accurate calorie estimate. Most wrong estimates fell far below the actual calorie count — as when a 590-calorie fajita was identified as a beef taco bearing between 192 and 289 calories.