I posted a similar picture in this thread:
http://theflatearthsociety.org/forum/index.php?topic=22119.msg453322#msg453322where there was a similar discussion to this one.
The usual explanation is that the window is convex or the camera lens is a fisheye.
A more complicated explanation is that light bends due to something or other to do with electromagnetic acceleration.
In all honesty, you can't really debate a picture like this unless you know the focal length of the lens used to take the picture. In my case, I did know, because at the time I took my picture, I only owned two lenses, neither of which was wide angle at all, let alone fisheye.
I would like to point out, however, that a piece of bent plexiglass is not the same thing as a lens. I've never seen an airplane window that was truly convex, only possibly bent slightly. We should easily be able to do experiments to determine if bent plexiglass causes any distortion of light.