My guess is that most technical users of MRtrix will use the latest Git version instead of upgrading when a new version is released. Given that some of these users will also be developing their own commands, it could be useful to store the Git commit hash in the image header, so that you can always work out what version of code you used to generate a set of results.

In fact we could store the version number instead if the hash corresponds to a tag.

What do you think?