One of the best things about McLuhan's tetrad or four laws of media is that a given medium can enhance, obsolesce, retrieve, and flip into multiple media. In case you'd like a quick refresher on the tetrad, it is an exploratory tool that McLuhan developed to help us make sense out of the emergence of media. Take radio, for example: It (1) enhances or amplifies sound (speech, music, etc) sent instantly across great distances simultaneously to lots of people; (2) obsolesces the written word as in newspapers as a mode of news delivery; (3) retrieves the spoken word that of course never really went away but was eclipsed to some extent by the products of the printing press; and radio, when it is pushed to its limits, (4) flips into television, which broadcasts like radio but re-inserts the visual into the mix. And, radio, the professional mass medium, also flips into podcasting that anyone with a microphone and a connection to the Internet can do. More on the tetrad in my book, Digital McLuhan, pictured below.
But back to photography: its flip into Snapchat is profound indeed, because permanency has always been one of photography's hallmarks. As Andre Bazin so aptly noted, a photograph rescues an image from "its proper corruption in time". In contrast, the Snapchat photo is deliberately intended to corrupt over time - and very quickly. Because the essence of Snapchat is that you send someone a photograph that you want him or her to see only when they receive it, and not any time after. If only former Congressman Anthony Weiner had known about Snapchat!
So we can now add Snapchat to the selfie as one of the media that photography has flipped into. Like a reflection in a pool of water, which can also be a selfie and also can disappear as soon as the person staring into the pool walks away, Snapchat epitomizes the ever percolating evolution of media to forms that are at once both new and well established in our past.
See also Marshall McLuhan and the Kindle and Tetrad on Eyeglasses Flipping into Google Glass
the spoken word
McLuhan and the Kindle | McLuhan and the Selfie