Non linear stretching

[anthony]

I think the better idea would be to try to extract the 'dive spot' locations and map that onto your image. may be a lot easier!

In any case the only non-linear stretching that Im acan do involved using Distortion maps, either absolute positional map
http://www.cit.gu.edu.au/~anthony/graph ... distortion

Or the IM composite displacement map.
http://www.cit.gu.edu.au/~anthony/graph ... /#displace

Neither will probbaly be usable as you have still have the problem of creating that displacement map.