Change header image in 2011 theme

Hi,

I can’t figure out how to use my own image for the header in the 2011 theme. In the customize theme section, to set a background I can upload my own background. But when I want to change the default header to one of my own, all I see is the several header images that come with the theme, but no way to upload my own header image.

Is that the way the theme is built, that is, you can’t use your own header image, or am I just not seeing how to do it?

Any help is greatly appreciated.

Thanks,
Martin