Google has launched a playful new app for Chromecast that lets a group of people create and draw on a collage of photos displayed on a TV. The app is called Photowall, and though it requires an iOS device to get started right now, anyone with a smartphone or a tablet can join in once its going. Once an iOS user launches Photowall, others will be able to visit a specific URL in Chrome to start adding their own photos to the collage and doodling on them.