Hmm. Well with some effort on your part, they are all "useable". The issue is that these images do not cover the entire universe. Only a subset, both horizontally and vertically, is included.

By rotating the EnvSphere 180 degrees, and carefully adjusting the Image_Map node's scales and offsets (with tiling turned off), you can make a partial panoramic photo map onto the correct subset of the sphere, so that straight lines become straight. You cannot zoom way out, though because you'll see the edges of the photo at top and bottom. And you can't rotate 360 degrees, because large sections are missing. If you're using the photo as a background, I suppose this is ok, but you won't get much in the way of reflections of things behind the camera, because there is nothing there. And you can't try to make a full environment IBL probe from it - too much is missing, particularly the sky, which is 80% of the light.

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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)