It looks like Google is trying to attract some of the Bing users who use the search engine for the background images on its homepage. Google has now introduced the ability to personalize your Google home page with a photo of your choosing.
Rather than have a daily image served to you like Bing does, Google lets you select an image from your computer, from your Picasa web photos, or from a public gallery it provides (also from Picasa). The gallery is rather extensive, and you can search it (though you are presented with a message saying, "Only select images that you have confirmed that you have the license to use.").
Google will be rolling out the feature to users in the U.S. over the next few days. You'll know when it's available to you because you'll see a lnk in the bottom lef-hand corner that says, "Change Background Image." Users in other countries will start seeing it shortly as well.
Images must be at least 800 x 600 pixels and in one of the following formats: .jpeg, .tif, .tiff, .bmp, .gif, .psd (Photoshop), .png, .tga, and selected RAW formats.
The feature is independent of iGoogle, Google's personal homepage feature.