Removing data from a digital file is sometimes easier said than done. Redacting PDFs has sometimes proven tricky (something the Acrobat team has worked to address), and now a research report notes methods for unscrambling numbers or text that have been obscured via simple Photoshop tricks. [Via]

I asked a few Photoshop engieneers for comments & got some useful nuggets:

• Gregg Wilensky says, "The ability to recover text that is blurred is limited by the amount of
  noise in the image (and knowledge of the blurring function). So, adding
  a bunch of noise to the image is better, but still not foolproof. I
  would suggest completely replacing the text with noise and blurring that
  (for aesthetics)."
• Jerry Harris notes, "Having a known set of limited targets, OCR numbers in his example, makes the
  reconstruction task a bit more realistic in terms of useful results than
  most."
• And Todor Georgiev writes, "Using a known set of blur kernels (those in Photoshop!),
  and a known set of targets, limits the set of possible outcomes
  and makes this technique work. But slightly change lighting
  and/or use custom blur filter, and your data is safe."