Recent Contributors
The Recent Contributors box shows portraits of folks who have edited that particular page. It is essentially a visual and personal representation of the wiki page's history. You can click a contributor's portrait to go to their personal page.
If a question mark is showing up instead of your portrait try re-uploading one this way. If a page has not yet been edited the Recent Contributors box invites the viewer to be the first to contribute.
See also: AboutUs Weblog post about Recent Contributors