Doesn't this already exist? Multiple times? Oh well, obvious 'exploit'. Wondering how Y! will react. They must've forseen this, right?
Question though, how large of a file can you hide with steganography in a 300mb picture?
Would that be big enough to hide an MP3?
On a side note, can you upload files to Flickr that have data appended after the end of the image data? Like people were doing on 4chan until moot removed that capability.