AutoWallpaper is an easy to use, multi-monitor capable desktop wallpaper changer for Windows (XP, Vista, Seven, Eight x32 and x64) and Mac OS X 10.4 – Lion.
AutoWallpaper revitalises your desktop by allowing you customise it like never before. Apply effects filters, such as greyscale, pixelate and blurring, to the entire image or just a section of the image.
Display wallpapers the way you want but specifying seperate categories of images for different monitors.
Personalise your desktop by adding photos to your desktop as Picture-In-Pictures.
And new in version 6.6; full support for Windows 8.1
Take a peak at the complete features listing.