A new update for Bing on iOS includes a neat little trick. Take a picture right inside the app, and Bing will send back a search for similar images.
Google, of course, has long had something similar: reverse image search, available for both desktop and mobile. But the mobile search is focused on images already on the web, while Bing's update seems more focused on searching for something you just discovered.
As VentureBeat points out, 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.