I solved my own problem. The background file was actaually found in the "C:\Windows\System32\imageres.dll" I had to extract it with program TGTSoft Resedit. I did this by navigating to image>5036>"änd selecting mspaint" as default editor for hex editor.
If anyone wants it i have it uploaded here.

This one is in jpeg format.

This one is in png format. Highest quality one.