Correctly implement a non-linear registration method.

[nfaggian]

Two interesting approaches for this:

1. J P Thirion (1998), Image matching as a diffusion process: an analogy with Maxwell's demons. Medical Image Analysis 2 (3) p. 243-260

• Effectively optical flow - looks very easy to implement and doesn't require a great deal of understanding about optimization.

2. Kybic, J., & Unser, M. (2003). Fast parametric elastic image registration. IEEE Transactions on Image Processing, 12(11), 1427-1442. Institute of Electrical and Electronics Engineers

• More closely ties in with the work in the codebase so far - partially implemented already.