Choose a Creative Commons photo from Flickr, crop it, and use it as your header. Attribution is added automatically!
To use the plugin, you must have a flickr API key. Sign up for one at: http://www.flickr.com/services/apps/create/apply
You must decide whether you will be using the plugin for commercial or non-commercial putposes, and choose the corresponding API key.
Once your template is updated and you have your API key:
From your site's Dashboard, go to "Appearance > Flickr Header", enter your API key and click "Update API key".
From the Network Dashboard, click "Settings > Flickr Header", enter your API key and hit "Update Key"