Advanced Background Changer that is totaly free, uses .bmp .jpg-files you can add an unlimited number of images to your imagelist. You can save differant lists for different sesons(e.g. christmas, summer, easter.. and so on) you reach most of the functions right from the system-tray (the field in the right bottom corner, right beside the clock) from the system tray you can also choose if the image should be stretched or title or centred.

Advanced Background Changer allows you to password-protect your settings.. when you go trough the images in your list in settings you can se the preview of the selected image and also choose to change to that image rightaway. as an extra settingsoption, you can have the program notify you when the image is being changed by playing a file (default or any wave-file on your harddrive)