There's a neat trick you can do with Mac OS X 10.4 and one of the free developer tools, Quartz Composer. You can create a movie that uses the built-in iSight camera to show a picture of you on a remote web page. You can even create something a little fancier. Of course, all data remains local, so there's no security risk.
But here's a variation.
1. Set the same webcam-enabled movie as the media texture for your land.
Now you can see a board with your face on it in SL. That's OK, nobody else can. The movie is client-side only.
2. Set some part of your avatar's skin, say, your head, to use the media texture.
Now you can see your own face on your avatar's head. Only you, so far.
3. Save the skin as a new item.
4. The picture won't update until you move the sliders, so keep jiggling them until you're happy.
5. When you're finally in the right position, hold really still, then press Save and Close.
The texture will now "bake". Other people can now see your picture on your avatar. You won't be able to save it; next time you edit appearance it'll be wiped.
So, if you have a Mac and want to check this out, head to my land in Caldbeck (218,26,40) and press play on the movie texture. The movie will play onto the Default Media Texture from the Library. Only one movie can show the iSight at one time, so close down the previous links if they're still open.
For everyone on PCs, and because nobody believes you unless it's on YouTube, here it is on YouTube. Music is original -- enjoy! The movie is CC-licensed.
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 License.