alt Hacker NewsYou can take TWO screenshots, moments apart, open in GIMP, paste one over the other and choose any one of these laying modes:
Lighten, Screen, Addition, Darken, Multiply, Linear burn, Hard Mix, Difference, Exclusion, Subtract, Grain Extract, Grain Merge, or Luminance.
Or just copy the text from the url. Not very secure, really. :D