I (over at Photosounder.com, home of the program that turns sounds into images and images into sound) have just started a new challenge. It consists in denoising a 115 year old sound by editing its image generated via Photosounder using Photoshop/GIMP/whatever you got or by writing a dedicated image processing algorithm.

The winners get a free license of Photosounder worth $140/€99.

Link to the contest with all the details, examples and files : http://photosounder.com/blog/2009/07/graphical-sound-denoising-challenge.html