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Why Blurring Sensitive Information is a Bad Choice for Hiding It

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KenR:
Here's an interesting post about how blurred-out information can be recovered

Undoubtedly you have all seen photographs of people on TV and online who have been blurred to hide faces. For example, here's one of Bill Gates:
[See Image Below]

For the most part this is all fine with peoples' faces as there isn't a convenient way to reverse the blur back into a photo so detailed that you can recognise the photo. So that's good if that is what you intended. However, many people also resort to blurring sensitive numbers and text. I'll illustrate why that is a BAD idea.

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...

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http://dheera.net/projects/blur.php

Deozaan:
Wow, that's cool.

f0dder:
Pretty interesting.

Blurring is so much prettier than just blocking out, though ;)

jgpaiva:
I think that there's also another issue: wouldn't the person who made the bluring algorith be able to reverse engineer it and get the original text?

f0dder:
I think that there's also another issue: wouldn't the person who made the bluring algorith be able to reverse engineer it and get the original text?
-jgpaiva (January 08, 2007, 05:16 AM)
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No, it's a lossy operation, so you won't be able to get the exact original. (Well, a malicious blur-tool author could do trick things with alpha channel in a 32bpp image, or perhaps some palette tricks for 8bpp, to make it a bit easier to get at original-ish data, but... that's pretty far-fetched).

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