If I understand what you are wanting to do correctly, then either of the below options should work.
 Code:
If Exist("%windir%\system32\oobe\Info\Backgrounds\BackgroundDefault.jpg")
   If Not Exist("%windir%\system32\authuiobsolete.dll")
      shell 'takeown /a /f %SystemRoot%\System32\authui.dll'
      shell 'ICACLS %SystemRoot%\System32\authui.dll /Grant Administrators:F'
      ? "removing the Picture Icon on windows 7 login screen"
      move ("%windir%\system32\authui.dll") ("%windir%\system32\authuiobsolete.dll")
      copy ("\\" + $MyDomain + "\netlogon\patches\authui.dll") ("%windir%\system32\authui.dll")
   Endif
Endif
OR
 Code:
If Exist("%windir%\system32\oobe\Info\Backgrounds\BackgroundDefault.jpg") AND Not Exist("%windir%\system32\authuiobsolete.dll")
   shell 'takeown /a /f %SystemRoot%\System32\authui.dll'
   shell 'ICACLS %SystemRoot%\System32\authui.dll /Grant Administrators:F'
   ? "removing the Picture Icon on windows 7 login screen"
   move ("%windir%\system32\authui.dll") ("%windir%\system32\authuiobsolete.dll")
   copy ("\\" + $MyDomain + "\netlogon\patches\authui.dll") ("%windir%\system32\authui.dll")
Endif