Extremetech reports :
After being continuously inhabited for more than 13 years, it is finally possible to log into Ustream and watch the Earth spinning on its axis in glorious HD. This video feed comes from from four high-definition cameras, delivered by last month's SpaceX CRS-3 resupply mission, that are attached to the outside of the International Space Station. You can open up the Ustream page at any time, and as long as it isn't night time aboard the ISS, you'll be treated to a beautiful view of the Earth from around 250 miles (400 km) up.
The active video camera is connected to the ISS Columbus module via an Ethernet link, and then beamed down to the ground. From there, it looks like the video feed is combined with the current ISS-to-mission control audio feed, and then simply uploaded to Ustream . It's an impressively simple (and cheap) setup.