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 working for me, but I couldn't find the motivation to adapt the build system to the new libraries. Drop me a line if you want this.