Need assistance with uploading background image

Hello all,

I'm researching a PoC to upload background images to the Azure sign in page using a delegated application. I've successfully been able to change the sign-in text and the background color but unable to determine how to upload a background image or banner logo via PowerShell or the Resource Graph Explorer.

The cmdlets I'm attempting is "update-mgorganizationalbranding".

References I'm using:

https://docs.microsoft.com/en-us/graph/api/resources/organizationalbrandingproperties?view=graph-rest-1.0#methods

https://docs.microsoft.com/en-us/powershell/module/microsoft.graph.identity.directorymanagement/update-mgorganizationbranding?view=graph-powershell-beta