I had an idea a few days ago where you authenticate your identity (i.e. numeric fingerprint) on-demand by sending a pic of yourself where the QR code is overlayed as blacked-out pixels before being transmitted. Then the recipient can look at the photo to see it hasn't been manipulated, and use the app to verify the QR codes match.

I'm sure there are issues with this, but it seems like a nice feature for when secure out-of-band communication is not possible.