title: Comparing files to identify ancestry & original source
body: <p>Assume I have 100 files, of which 10 are the originals and the remaining are revisions and/or combinations of the originals (Imagine a git tree). Given any descendant file, how can I identify the file that is most likely the original source? Does the process change if there are 1m documents? 100m documents? </p>
  
  <p>(This isn't homework -- just a non-programmer who can't find the right approach via google ;) )</p>