If you don't want to see the console pop up when the script runs, you might find useful information at How to hide/inhibit the console window when launching a Perl script on Windows?. First suggestion listed about leverage Win32::GUI is what I was thinking of.

One note of caution about having script that's trying to do something with the wallpaper and have it set for "Run whether the user is logged on or not". If no user is logged in, there is no GUI environment. (Learned this the hard way some time ago when I was trying to automate GUI based programs.) So if Task Scheduler tries to run this type of script with no user logged in, you might not get the results that you expect.