That is true - mutual information is one of the available methods in the Align module. On another forum topic (Loading images sequentially with overlap) you can see Lee’s suggestion for how you might align images from one frame to another (whereas my suggestion on that topic only would allow you to align each subsequent image to the first image in the stack).
However, it seems that you wish to report the mutual information score, not just use the mutual information method to align images. At present, that is not a measurement we imagined very many people would actually want to see! The only output for the Align module is the X and Y shift that results in the best alignment.
Please let us know if you are still interested in this score and we could consider adding it to our list of requested features.