Um, ok?
The user content files store no information to detect players WITHIN a given screenshot. The only note-able player information is stores is the user that created the screenshot, the user who last modified it, and the EXIF data embedded in the jpg.
I may be wrong though, it has been a while since I looked into any of the tags.

Also, is it just me reading the info incorrectly in Hex Workshop or do screenshots now seem to store some basic Map and Player information?

It is called Exif data, it is used as one of the precautions that bungie took to screenshot exploits. And to give bungie some sense of exclusiveness once halo reach screenshots start flooding the internet.

Read up

Also, the _blf format is used for nearly every external tag system. All tags between the _blf header and _eof footer is included in that file's tag system. In which the BLF header stores the name of the file, sometimes in several different languages. Other than that, the format for all blf files are essentially the same.
Read up

This C# library will allow you to load any halo reach user content file into a neat object to access its data. It will only read, and not write. From the looks of things, Bungie has made a lot of consideration into user exploitation. The Tag object stores an array of nested tags that can be accessed like so:

Tag[0]

To return the tag in the first index.
Or the much nicer:

Tag["chdr"]

Which would return the tag named "chdr".

A tag object contains 3 feilds.
Name, a 4 character ASCII string which contains the tag name
Size, an Int32 which stores the size of the entire tag(Including the name and size bytes)
Data, a byte array containing the tag's information.

The Data field can be accessed via byte array or BinaryReader.

Tag files can be initialized either directly from a STFS file(using DJ SkunkieButt's X360 Library), or from an already extracted file, and even directly from a stream.
Here is an example of me loading a Tag from a STFS(con) file.

Derp = new Tag();
                Derp.LoadFromSTFS(openFileDialog1.FileName);

Included in the download is the Library its self, along with the source of an application that shows how to use it properly.


I only ask that you give credit to me and DJ SkunkieButt for its use, and maybe add some of your tag research to the modhalo wiki.
Have fun.



Download

Those are 2 years old and have been circulating around the net for so damn long. Don't think you are special just because you have these.

New render.

I GOT A NEW TABLET SO I MADE THIS!

:S

im confused, your modeling a map, fur wut reason,,,,?