Changing desktop background

I'm running a Windows 8.1 system with Secure Lockdown v2.  I would like to change the background image to be a custom one, but am not sure where it is getting the default background image that it displays.

Can anyone provide a path or more information on which image is being used for the default desktop when the program is running?  Note I do not disable the desktop, so I see the usual windows one.  I want to edit that file and add some text which will be displayed in kiosk mode.

Thanks,
Alex

Secure Lockdown will take the image Windows uses in its Desktop background setting. It will only do this if the System Lockdown > Local Level > No Desktop option is enabled.