Taken from the top of Europe, Jungfraujoch in Switzerland.
The curvature isn't that of the earth, of course, but comes from the panorama processing.
I take no credit for this photo.
Here's the link to the creator and the original picture fro DeviantArt: http://erezmarom.deviantart.com/art/Curvature-of-the-Earth-165243474
