Cool! I have been getting tired of the standard desktop pictures built-in from Apple. I used to be someone that would customize my Mac all the time, but now I don't make enough time for it. Wallcat is easy because you just launch it, tell it to launch itself on startup and that's it! You'll have a funny looking cat icon in your menu bar.
Tip: If launching the app doesn't change the desktop picture right away, quick it and relaunch. That worked for me.