The only way to *really* determine the value of a note
is to have a reasonably qualified person look at the note.
Sometimes a collector will send a photocopy of both sides
of a note for identification rather than the note itself.
If you want a best effort, members of rec.collecting.paper-money
can almost always identify a note, given enough information
about it.  See the "I found a note from country XYZZY" section
for what information to include about the note.