Bing Visual Search
No app required, well, that's if you have a Windows Phone. In that case than its already built in.
Let's say you're meeting with a friend and shes rocking a killer pair of shoes she just bought at Bloomingdales. You need them in your life, but for a better price of course.
Well, all you have to do it point your camera at the barcode, snap a picture and Bing will bring up all the information about the product for you; where to buy it, price comparisons etc..
Cost: Nothing, it's built in!
Available for Windows Phone
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