Another feature of Keybase's exploding messages is that when they expire, the text is replaced by the md5sum of the message. So a faked screenshot can (potentially; I haven't verified this) be proven to be faked by appealing to the md5sum in its place, crucially, without needing to reveal the contents of the original message.

Sorry, I was wrong. I misread in a chat thread on KB something about md5s. Can't find it now because no searching in KB (yet!).

Exploded messages are just replaced with an image of what people are calling 'ashes'.

Further conversation on KB about this points out that hashing the message would compromise the secrecy. I still think it would be a neat feature.

That would only work if everything else about the photo was identical - device, resolution, carrier, time, battery level. Seems very unlikely one could substitute even identical text in a screenshot with enough accuracy to get the same hash from an image file.

The md5sum would be of the message itself, not the illicit screenshot.

That makes sense. I think my HN incoherence limit was exceeded here at 2 am.