It's not that you can unredact them from scratch (you could never get the blue circle back from this software). It's that you can tell which of the redacted images is which of the origin images. Investigative teams often find themselves in a situation where they have all four images, but need to work out which redacted files are which of the origins. Take for example, where headed paper is otherwise entirely redacted.

So with this technique, you can definitively say "Redacted-file-A is definitely a redacted version of Origin-file-A". Super useful for identifying forgeries in a stack of otherwise legitimate files.

Also good for for saying "the date on origin-file-B is 1993, and the file you've presented as evidence is provable as origin-file-b, so you definitely know of [whatever event] in 1993".