I like the OpenWeatherMap idea, and the API seems relatively sane, but how does it get to display a

I like the OpenWeatherMap idea, and the API seems relatively sane, but how does it get to display a picture of what the clear blue sky really looks like today, along with a "cloudiness: 71%" statistic.

http://openweathermap.org/city/2179537 

I guess that's the "Beta" part of it.