Data is not annotations. Yes - there are huge amounts of data anticipated - of course there are - and of course I'm aware of that. That has NOTHING to do with annotating images. Nothing.
There are PDS conventions for describing data - as I am sure you are aware - but, I say again, annotations are massively diverse things from scales to grids to labels to arrows to paths to sites to directions to layers to bedforms to routes to dunes etc etc - and all of these are done by JPL, Cornell, ESA, ESOC, SWRI, ASU, CICLOPS, HRSC, MPI, dozens of institutions annotating thousands of things in a million different way - there can be no convention on how to do that. Even two people doing exactly the same thing, do it differently.http://marsrovers.jpl.nasa.gov/mission/tm-...l1813_1_br2.jpg
is different to http://marsrovers.jpl.nasa.gov/mission/tm-...l1687_2_br2.jpg
I would say you're looking for something that doesn't exist, and is impossible to establish. It's like trying to have one set of rules, for every sport in the world - from Football to F1. You need to better specify exactly what you mean by annotations before you can progress.