Unfortunately the Bing Vision feature has been removed from Windows 10 Mobile for now. There's currently no official statement from Microsoft whether it will be added later or not.
There are already several requests to bring back Bing Vision in the Windows Feedback app you might want to vote for.
Until then you would have to use a 3rd party app from the ...
The Bing Vision app is obscurely available under the camera app.
First open the Camera application, then click the settings icon, to open this view:
Click on the Lenses option, and...voila
Bing Vision will be available, amongst all the other lenses and camera related applications, as shown above.
It appears, after having gradually been pushed into the background and having its functionality reduced, Bing Vision is being killed off. I haven't found any official announcements from Microsoft yet, but Windows Central has a few articles covering the saga.
According to Windows Central, in Windows Phone 8, Bing Vision could scan: