Aka23,
I can partly understand the privacy issue, but if you're actually considering online dating with a picture included, then just go with a regular picture. Or maybe make it a bit more artsy with half of your face shadowed or something. I wouldn't go with trying to distort your features too much, and even if you put on glasses/grow a beard, most likely the people who know you will still be able to recognise you. Don't really see a problem if they do. If you don't want people do know you're doing personals, don't go with a picture at all (if they allow you to) and mention picture will be provided if asked for.
I've dated a couple of guys I met online, and one guy didn't wear glasses in his pic. When I met him he did, and to this day I think he looks quite different than without his glasses. So, that might work for you. As long as it's an actual pic of you, that's what matters. Don't mind pics that emphasis your "good side", but I'd rather not expect Brad Pitt and end up with Ozzy Osbourne... Honesty is much better.
Just my $0.02