I used Hachoir (https://github.com/haypo/hachoir3), a Python library that I've contributed to. Hachoir disassembles files using a library of parsers, with the intent of describing the function of every single bit in the file. You can see the resulting disassemblies (rendered with the hachoir-wx GUI) here: http://imgur.com/a/F1cnV
What an incredible tool... I have a webapp that has as a small component the analysis of JPEG metadata, this will be very useful for future development.
I use Hachoir for a lot of tasks - digital forensics (examining file tables on a filesystem, discovering slack space taken up by hidden data, etc.); for metadata extraction (for which the hachoir-metadata subproject is designed); for file carving (either with hachoir-subfile or manually); and just to geek out about file formats (did you know .doc/.ppt is secretly a FAT filesystem?).
Funny, I had no idea it could do all that. I've been using it in production for years to extract width/height/duration of media files at compile time so my loading placeholders are perfectly sized at runtime in a basic web app.
