How to Recover Numbers from Blurred Images

Yikes.

Suppose someone posted a photo of their check or credit card online for whatever awful reason (proving to Digg that I earned a million dollars, showing something funny about a check, comparing the size of something to a credit card, etc.), blurring out the image with the far-too-common mosaic effect to hide the numbers:

Seem secure because nobody can read the numbers anymore? WRONG. Here’s a way to attack this scheme:

(via Schneier on Security)

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