Of course I've heard of the Obfuscated C Contest, but this is the first I've heard of the Underhanded one - so cool:
The general theme of the contest is to write "sneaky" code that's difficult to spot at a glance. This year's specifics are to write a program that takes an image and a set of rectangles, and "censors" those parts of the image which are represented by the rectangles.
But that's not really underhanded, is it? The sneaky part comes in here: Your program needs to make that censored data somehow recoverable, and needs to pass basic scrutiny (say, a peer code review).
Writing a program that looks like it censors the data, but actually leaves it recoverable - that's not hard. But doing it so it looks like it isn't... That's genius.
Looking forward to the results!