The design/layout of hellorobot.org is a modified version of the Grid Focus WordPress theme – a fairly extensive modification, but the same basic structure. And although this blog is a smaller width and uses a different menu style, adding a header image to the default Grid Focus theme is not much different than it was here.
I think you’ll find that adding a header image is pretty simple, really. It requires editing two files: first, the header.php file; and second, the style.css file. Both are found in the ../wp-content/themes/grid_focus_public/ folder. You can edit these files in a simple text editor like Notepad on Windows or TextEdit in Mac OS.