Google Now on Tap is a new feature of Android 6.0 which doesn't seem to be getting much attention yet. Essentially you can press and hold the home button on any screen and the app will try to find useful things to do for you. For example if you're reading something online an an actor's name is mentioned you could press the button and find other pop up search results for their name.
Now on Tap is getting more features today with the ability to scan photos. The idea is that you can just take a picture of a poster or a business card for example and then pop into the gallery view. From there, press and hold the home button and Now on Tap will scan the image and pick out things like the name of an artist or the phone number on the card. Then you can take further action like searching the web or making a phone call.
We've tried it a couple of time with varying results - some very easy to read text has been identified but not a lot else at the moment. Google hasn't officially talked about these features yet to it's likely that they're not quite ready for publis use, but there's definitely potential in seeing how it could work in the future. Give it a try right now on Android 6.0!