Leaky redaction

Yay! Third place in the 2008 Underhanded C Contest.

The Underhanded C Contest is about writing a program that would pass a code review, but secretly does evil things, and where the covert behaviour can plausibly be explained away as a bug. This year's challenge was to write a program that would black out one or more rectangles of an image, but secretly retain the information somewhere in the output image. The results were announced today, and apparently I got a third place! Do check it out, the winning entry is really clever!

Here is my contribution:

• leaky_redaction_linus_akesson (Tarball, 1496 bytes)