With this original image, we first
perform a shear along the x-axis.
With this original image, we first
perform a shear along the x-axis.
This results in an image which has its vertical edges aligned correctly.
The second stage is a shear along the y-axis. 
The final image should be oriented
correctly, with slight error
that depends upon the original skew of the image. This algorithm
based on work done
by Fateman and his students in 1995.