I have a domain controller running Windows Server 2008 R2 Standard.
Question:
Are all Windows 7 Group Policy objects applicable to Windows 8 and Windows 10?
OR
Do I need to create a separate policy for Windows 8 and Windows 10 PCs on the Windows Server 2008 R2 Standard domain controller?
Recently, I changed wallpaper on the group policy but it has not been reflected on Windows 10 PCs.
What do I need to do to resolve this issue? Do I need to migrate my domain controller to Windows Server 2012 to resolve this problem?
The OS compatibility of a particular policy setting varies from setting to setting. The Group Policy Management console will indicate the OS compatibility in the policy item's description. In general, the answer is yes. But there are also some policy settings that only apply to specific OS versions.
I don't know specifically about the compatibility of the wallpaper setting. But it's in your best interest to download the Windows 10 Administrative Templates and add them to your Central Store. You may find a Windows 10 specific wallpaper setting. And if so, you can add it to the same policy you're already using and each OS will just use the policy that it understands.
You do not need to upgrade your domain controllers to apply group policy to newer Windows desktop OSes.