For some file types, e.g. images and sound, I would like to also add some local sensitive hash (LSH), and be able to find duplicates that way. E.g. that would allow me to find duplicate images where the image metadata was changed, or maybe the quality was changed, etc.

Ideally, I would want to add such meta data to Git-Annex. I'm not sure if this should be a backend (backends) or kept separate from it (as there will be collisions, by design).

I also want fast lookups for some specific hash. I'm not sure if the Git-Annex metadata allow for that? A Git-Annex backend naturally has this feature, but then how would it handle collisions? I would want that this LSH backend just links to a list of matching files, i.e. symlinks to the real files (via SHA backend or so).

Is anything like that already supported?

If not, would it be possible to add such support to Git-Annex? How?