This method neatly demonstrates gradient-based direct image alignment: it fits a a target image to a reference image using a homography.
However, it also includes some great software for use in other projects:
Autodiff - fairly comprehensive auto differentiation class, to dramatically simplify and speed up development of gradient-based optimization.
Lie - Lie algebra class supporting various geometric groups, which also supports auto differentiation.
Ojw_interp2 - Fast mex-based image and gradient sampling, which also supports auto differentiation. Mex this function first by calling "mex ojw_interp2.cpp" in the directory you installed the files from this submission in.