These are the profile images that every new user here receives. How are they made? I mean, are they randomly formed in some way? I could use something like that.
These are gravitators ("globally recognizable avatars"). Gravatar is a free web service.
See http://www.gravatar.com/ .
Setting up Gravatars on your site is simple; you don’t even need an account! Plugins are available for leading blogging programs and content management systems, and our tutorials will help you launch Gravatars quickly.
linux identicon:
identicon
$ curl -s "http://www.gravatar.com/avatar/`uuidgen | md5sum | awk '{print $1}'`?s=64&d=identicon&r=PG" | display