- Your computer. You select a list of folders that contain photos and Google Screensaver monitors the JPEGs from these folders.
- Picasa Web Albums. If you use Google's photo sharing site, you can view pictures from the most recently modified albums and from your contacts. It's probably the most interesting feature of Picasa Web Albums: you can monitor all the photos uploaded to your contacts' albums.
- Web feeds. You can find them in photo sharing sites like Flickr, Picasa Web Albums or at this page. Some nice feeds: Flickr (Vista wallpapers, nature, architecture, landscape, Google food), Yahoo search (autumn, Dali, sunset) . To add a new source, right-click a link to a feed in IE and Firefox and select "Add to Google Photos Screensaver".
The screensaver acts like a slideshow so you can move to the next/previous photo using the mouse. The title and the author of a photo is always visible and you can go to the source of the photo by clicking to one of the links from the bottom of the window.
You can configure the visual effects (collage, wipe, pan and zoom, cross fade) and how often the photos change.
The screensaver is a part of Google Pack, but if you get it from this page you can install only the screensaver. Then you can uninstall Google Updater and keep the screensaver.
Update. You can download Google Screensaver without installing Google Pack (this link may change in the future):
gpdl.google.com/installers/ci_ss/en/2.2007.0412.1728/gpscrsav.msi (4.5 MB).
Update 2. Here's a more recent version of the screensaver: http://dl.google.com/packdata/ci_ss/3.1.0.7112/en/setup.msi.