To add a background image to your Google search page, just click on the unassuming “Change Image Background” link in the lower-left corner of the site. You will have the option of uploading a picture from your Picasa account, your hard drive or a set of stock images provided by Google. It’s a pretty simple process, you just select your photo, click upload and voila, Google become a split image of Bing.com
You will noticed that Google's logo turned white as well. This new "Change Image Background" selector feature is only available in Google.com. It will takes a few days before the feature is rollout to other Google.xxx extension.