We've been waiting for Backdrops to hit our devices since the announcement back in summer at Google I/O which they said was coming "soon". Back then, little did we know that "soon" was months away. We're learning, Google.
Rant aside, you can opt to display the weather on your television, as well as art, satellite images and featured photos shared on Google+. Since the debut of Chromecast last year, beautiful background images have graced our screens, but now with the ability to pick and choose whether our Google+ photos are cast (off by default) and other categories. It's a great way to spice up the experience in-between casting sessions.
Of course, you'll need to purchase a Chromecast and have the latest version of the Chromecast app (which is rolling out now) installed to enjoy.
Source: Google Chrome Blog