alot of us do know what each other look like. In the old days of ChatterBank we were forever posting pics of our mugs.
Now alot of people (especially on B&S) still post their Mypace addresses which has links to their pics on. Or they swap email addresses and show them via that way.
So in a round about way of answering your question, not many of us have that 'mystique' anymore.
In the 'old' days, before myspace and similar, I was given an image of a tweedy gentleman with a houndstooth sports jacket and a pipe. i am actually as far away from that as I can be - so I was happy to correct the image, but only verbally. I loathe having my picture taken as I have a seriously low self-image physically, so I would never put a pic out there on the web.
I wish we could have signature bars like other message boards and avatars. I wouldn't mind posting my pic then and yeah I'd like to see other people's sig bars as I think your choice of photo ( self and others ) and art that you've created yourself tells a lot about people.
In A Pickle once persuaded me to post a picture of myself by describing me as 'cute'. I posted a picture showing me (wearing specs) with a large python around my shoulders. The reply I got read as follows: "Well, thanks for the pic, I still think you are cute, but I'd dump the guy in the glasses if I were you!" After that, I think I'm safer not posting any pics of myself ;-)