[chocolatkey]

This was a great post with references to many tricks and tools I was not aware of that might help me in similar endeavors. Do you have any particular advice for reverse engineering image data files (not encrypted, of a completely proprietary format)?

[breadbox]

I'm afraid that's something I don't have any experience with. However, another commenter mentioned a cool video he did on just this subject, at https://news.ycombinator.com/item?id=21728298 -- so maybe check that out?