A few usability improvements are hitting the Chromecast app with the latest update.
The new version of the app displays your current Chromecasts in a larger "card" style, with quick access to the settings and backdrops on each. You still have the same settings for managing your own backdrop images, but now no matter the source you'll be able to see a history of the last five images that the Chromecast has displayed while on standby. Each image will give you convenient links to view the source, as well as the Google+ profile of the photographer if there is one.
Deeper in the backdrop settings you can now choose the speed at which the Chromecast moves through backdrop images, at either half, full, or double speed. You don't need an update to your Chromecast for this, just snag the latest Chromecast app in the Play Store for your phone or tablet.