The latest update for Bing on iOS brings image search by taking a photo. Take a picture right inside the app, and Bing will send back a search for similar images.
Google has similar image search which is available for both desktop and mobile. Google mobile image search is focused on images already on the web while Bing for iOS update seems more focused on searching for something you just discovered.
This may be more in line with Google Goggles, an image search app that similarly allows users to search after taking a photo. But that only provides informative suggestions and hasn’t been updated in some time. So if it’s a feature you’re after, Bing might be worth a shot.