Why (or why not) can't we (AG community, everyone by "we" post pictures on our profile. wait no....it chould end with a "?" right? haha i ended with one on the one :S
Well, I think it would probably be a lot more work for the people who run the site and the mods. They would have to develop some system of recognizing a certain point in the internet(a chosen picture, for example) and they would have to figure out how to move it around with the user, wherever he/she posts. The mods would also have to keep a watchful eye out on any innapropriate pictures, and that's not always really easy.
We have enough to worry about the server crashing with all the games takes up server. And the users. I don't think adding profile images would be the best idea.
Other than all the space, people could take the images and post them on other sites, and who knows what sites these may as well be. They can take your picture, put it up on a social networking site(e.g. MySpace) and people could start thinking that that person is you. They can edit your picture and make you some sort of freak. There are probably a lot more to think about, but those are other reasons why not to post images of yourself.
