this is insane....how the hell does this work!! (instructions below) Save PNG. Open in Photoshop. Save as RAW, with all default settings. Change extension to MP3 (To do this when you pick save as .RAW in photoshop just put .mp3 at the end of the file name) Play in Winamp.
My guess is binary...series of zeros and ones...changing the format of how a computer (app) reads the codes via the extension would be my guess...
I'm pretty sure it's just embedded files. Kinda like how you can embed .rar's with mp3's or something into normal .jpgs.
The picture is like the digital coding of it, like word in an essay. Try drawing on it and repeat the process above and it wont play past the changes you do.