So, I came across this nifty program a while back.
MP3NEMA
You can hide (and extract hidden) files in mp3s, tucked away between frames.
Put images, pdfs, whatever... Though, they should be small so as to not arouse suspicion (such as a 4 min 128k mp3 that is 30MB, ha). There are a few ways to digitally watermark files but this seemed a cool, unique (and personal) route.
My original idea stems from giving mp3s to people and finding out they've given the files to others when I've specified I don't want them to be out. I've even given a song to only one person, later found it on the net, and had them adamantly deny any involvement!
So I was thinking to make a text file with the persons name, and hide it in the frames - like personalizing it for them. If they mess with the mp3 tagging the file will still stay there unless they totally re-encode it (unlikely... unless this gets popular, haha). If I see the track floating around online or someone tells me they have it I can just extract the txt file and see who it originated from.
You could also do this in a non-paranoid way and just trace the path of your files.
For instance: say I post an mp3 on a few message boards (with a file hidden with the name of the board). A few months later I can go on Soulseek or wherever, download my track from a few different people, open the data, and gather the stats.
This info would be very handy for future promotions and/or deciding where it is worth while to post.
Another idea I had was to hide an mp3 within an mp3. If the track only originated from you (not released) with the hidden file then you could distribute this, wait quite a long time, and then announce that there is a whole other tune that can be extracted. Kind of like a modern version of the hidden track on a CD, ha.
Even this is an extended version of another project I had years ago. I was making/molding records out of high performance resins. I don't want to get into a lengthy explanation on that but suffice it to say I had the process down perfectly. I then had Ron Murphy at NSC cut me an acetate of a track within 2 1/2 inches of the spindle, pretty much where the label is on a record, and built a mold around that. With the absolute thinnest layer of resin on the acetate I would set an audio CD label side down (into the mold) to cure. After many trails I finally perfected it - a CD that plays (still thin enough for even my front-loading car stereo_ yet has one analog recording molded into the face that can be played on a turntable.
In the pic below you should be able to the the grooves in the light reflection.
