Hello,
I have found this link that maybe ansver to your question :
Wallpaper Changer[
^]
carefully,carefully,carefully :)
Read the Article, watch out for "See also.." on the right column of the web page, there are many other solutions.
I was surprised how many softwer solutions I found within so little time I have been member of codeproject,
just exploring the Articles.
All the best,
Perić Željko