HiddenTask.vbs

Option Explicit
Dim args
args = """" & WScript.Arguments(0) & """"
Dim i
Dim temp
For i = 1 to WScript.Arguments.Count - 1
    temp = WScript.Arguments(i)
    temp = Replace(temp, " ", "")
    temp = Replace(temp, "	", "")
    temp = Replace(temp, "^", "")
    temp = Replace(temp, "&", "")
    temp = Replace(temp, "|", "")
    temp = Replace(temp, "<", "")
    temp = Replace(temp, ">", "")
    temp = Replace(temp, "%", "")
    If StrComp(WScript.Arguments(i), temp) = 0 Then
        args = args & " " & WScript.Arguments(i)
    Else
        args = args & " """ & WScript.Arguments(i) & """"
    End If
Next
Dim WshShell
Set WshShell = WScript.CreateObject("WScript.Shell")
Dim obj
obj = WshShell.Run(args, 0, False)
Set WshShell = Nothing
WScript.Quit

OldestSlideshow.xml

$pick = ls -recurse -include *.bmp,*.jpg,*.png | sort lastwritetime | select -index 0; (ls $pick).LastWriteTime = Get-Date;

ShuffleOldestSlideshow.xml

$deck = ls -recurse -include *.bmp,*.jpg,*.png | sort lastwritetime | select -first 3; $index = get-random -minimum 0 -maximum $deck.count; $pick = ls $deck | select -index $index; (ls $pick).LastWriteTime = Get-Date;

ShuffleSlideshow.xml

<?xml version="1.0" encoding="UTF-16"?>
<Task version="1.3" xmlns="http://schemas.microsoft.com/windows/2004/02/mit/task">
  <RegistrationInfo>
    <Date>2015-02-11T10:06:22.6992337</Date>
    <Author>DavidRuhmann</Author>
  </RegistrationInfo>
  <Triggers>
    <TimeTrigger>
      <Repetition>
        <Interval>PT20M</Interval>
        <StopAtDurationEnd>false</StopAtDurationEnd>
      </Repetition>
      <StartBoundary>2015-02-11T10:05:17.837334</StartBoundary>
      <ExecutionTimeLimit>PT2M</ExecutionTimeLimit>
      <Enabled>true</Enabled>
    </TimeTrigger>
  </Triggers>
  <Principals>
    <Principal id="Author">
      <UserId>User</UserId>
      <LogonType>InteractiveToken</LogonType>
      <RunLevel>LeastPrivilege</RunLevel>
    </Principal>
  </Principals>
  <Settings>
    <MultipleInstancesPolicy>StopExisting</MultipleInstancesPolicy>
    <DisallowStartIfOnBatteries>false</DisallowStartIfOnBatteries>
    <StopIfGoingOnBatteries>true</StopIfGoingOnBatteries>
    <AllowHardTerminate>true</AllowHardTerminate>
    <StartWhenAvailable>false</StartWhenAvailable>
    <RunOnlyIfNetworkAvailable>false</RunOnlyIfNetworkAvailable>
    <IdleSettings>
      <StopOnIdleEnd>true</StopOnIdleEnd>
      <RestartOnIdle>false</RestartOnIdle>
    </IdleSettings>
    <AllowStartOnDemand>true</AllowStartOnDemand>
    <Enabled>true</Enabled>
    <Hidden>true</Hidden>
    <RunOnlyIfIdle>false</RunOnlyIfIdle>
    <DisallowStartOnRemoteAppSession>false</DisallowStartOnRemoteAppSession>
    <UseUnifiedSchedulingEngine>false</UseUnifiedSchedulingEngine>
    <WakeToRun>false</WakeToRun>
    <ExecutionTimeLimit>PT2M</ExecutionTimeLimit>
    <Priority>7</Priority>
  </Settings>
  <Actions Context="Author">
    <Exec>
      <Command>HiddenTask.vbs</Command>
      <Arguments>powershell -command "$total = ls -recurse -include *.bmp,*.jpg,*.png | measure | select count; $index = get-random -minimum 1 -maximum $total.count; $pick = ls -recurse -include *.bmp,*.jpg,*.png | select -index $index; set-itemproperty -path 'HKCU:Control Panel\Desktop' -name wallpaper -value $pick.fullname; $path = $env:appdata + '\Microsoft\Windows\Themes'; $tw = $path + '\TranscodedWallpaper'; $ini = $path + '\slideshow.ini'; del $tw; clc $ini; $signature = '[DllImport(' + [char]0x22 + 'user32.dll' + [char]0x22 +', SetLastError = true, CharSet = CharSet.Auto)] public static extern int SystemParametersInfo(int uAction, int uParam, string lpvParam, int fuWinIni);'; $type = Add-Type -MemberDefinition $signature -Name Win32Utils -Namespace SystemParametersInfo -PassThru; $type::SystemParametersInfo(20, 0, $pick.fullname, 0x01 -bor 0x02); rundll32.exe user32.dll, UpdatePerUserSystemParameters;"</Arguments>
      <WorkingDirectory>%UserProfile%\Pictures\Backgrounds\Show</WorkingDirectory>
    </Exec>
  </Actions>
</Task>

To Use

1. Save HiddenTask.vbs (Optional, without hidden task the cmd prompt will display every event)
2. Import Desired Scheduled Task XML
3. Update UserId in the scheduled task to use your user DomainOrMachine\Username
4. Update the background image folder location WorkingDirectory

There are two more registry keys that can be set to control the wallpaper style

Notes for myself for powershell transition idea (fade): show borderless form of new image on each monitor with 0% opacity then using a timer, transition the opacity to 100, when 100 change wallpaper and close form.

hiddentask.vbs gives a runtime error on windows 10, line 3 char 1, subscript out of range code 800A0009