one of the "underhanded c" contest winners many years ago was an entry for a redaction tool, which drew black boxes on an image in such a way that the software developer could later effectively recover the redacted information easily, while still being able to claim plausible deniability. The trick was that it worked by producing a ppm file where pixels with single digits would become zeros, but double digits would become 00, and three digit ints would become 000 (all valid values for black in ppm).

Reminds me of an old Perl module which translated code into a trinary alphabet with the characters space, tab, and new line. The resulting coded file is just an import statement and whitespace, but runs just fine.

Here is the link if anyone's interested: http://notanumber.net/archives/54/underhanded-c-the-leaky-re...

Wait, shit I have totally done this. God damn it. Fortunately nothing super sensitive but damn.

Interesting. I recently hacked together a tool shows the area on the screen I point to in maximum threshold, to make things like this visible. I have it mapped to a hotkey and I fire it up every time I see a redacted area.

https://github.com/guidovranken/threshold-zoom

Non-AMP link: https://9to5mac.com/2018/03/13/ios-markup-reveal-redact-sens...