It takes one or more directories with images as a parameter (no GUI) and sets a randomly chosen image as background. If there is a border remaining, its color is the average color of two corners of the image. This mostly fits the image very well.
The program does not work if the root-window is hidden by another program that does not pick up changes on the root-window.
I wrote zufall because chbg, the program I used before, was the only GTK1-dependency left on my desktop. Also, I really disliked the background-colors chbg's "random-background"-feature gave me most of the time. Maybe it's useful to you.Xinerama support (i.e. multiple screens) is on its way! Check back in some time if you need this.
Zufall was mentioned in the Magazin Linux User. The article is available in german (html) and english (pdf).