Note: please refrain from commenting on Telegram's design of OTHER parts, as it will distract from the stem of the question.
Signal (Previously, "TextSecure" app) uses specific "Your identity / Their identity" type of verification to verify a secure channel.
Telegram, on the other hand, displays a picture of pixel-like array with different colors and a set of alpha-numeric characters under it, different from each secure channel (i.e. "Secret Chat"); if these pictures or alpha-numeric characters match on both ends of the parties' phones, then the Secret Chat is "200% secure" [sic].
In Telegram, how is the verification picture generated? What makes it secure? And what makes MITM on key exchange "200%" impossible when that picture is matching on each phone?
Merit of question:
Signal clearly displays the fingerprint of my own key (which I have on my own phone) making this very sensible, as if it matched what THEY saw as my fingerprint, then it's physically and technically impossible that a MITM happened.
What in Telegram's design ensures this same outcome as with Signal?
This question needs an answer as, indeed, now even Whatsapp (using "TextSecure" encryption protocol) displays ONE set of numbers that has to be matched on both ends of the conversing parties.