Once I read that it is possible to code mp3 files into an image format (let's say .png), and to decode the image file into the mp3 back again. However, I lost that link, and now I can't find good info about this.
Three questions for you folks: Is this really possible? Does it make sense? Would it decrease considerably the mp3 file size?
Is this really possible?
Yes - you can use anything as a source for the colours in an image.
Does it make sense?
Not really - the image wouldn't look good, and the music wouldn't be easily playable. The only likely reason for doing this is steganography, i.e. hiding the mp3 inside an image of something else so that it's not easily detected.
Would it decrease considerably the mp3 file size?
No, the file size would almost certainly be larger than the original (and much larger in the steganography case).