Before launch the next version of Walyk Wallpaper Changer I want to inform you that is in progress the development of a new module to manage layers for Wallpapers. With this external module you will be able to design calendar themes and you might create other kinds of layer that can be combined with your wallpapers, for example: quotes of the day (including different graphics elements). At the moment you could use PNG an JPG files. I personally recommend to use PNG files with alpha transparency support because you can use clip-arts that contains shadows and transparencies.
This is a earlier version and could take me one month or two to finishing the development.