Lambda the Ultimate

Inspired by Daniel Horn's Obfuscated V contest in the fall of 2004, we hereby announce an annual contest to write innocent-looking C code implementing malicious behavior. In many ways this is the exact opposite of the Obfuscated C Code Contest: in this contest you must write code that is as readable, clear, innocent and straightforward as possible, and yet it must fail to perform at its apparent function. To be more specific, it should do something subtly evil.

I wasn't aware of this contest. This concept sounds like fun, the idea being to write source code that easily passes visual inspection by other programmers.

The challenge for the first UCC is to write a simple program that performs some basic image-processing operation, for example smoothing or resampling, but manages to conceal a unique imperceptible fingerprint in each image it outputs.