You can get the image I used here:

http://www.flickr.com/photos/simons/2057438156/

Try it yourself.

And let me assure you that this has nothing to do with it being an indoor scene. The same is produced with an outdoor photo. If necessary, I'll render that, too.

In what way is the curvature of the sphere is visible?

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)