Its very simple... follow these steps:
[{BE098140-A513-11D0-A3A4-00C04FD706EC}]- open the folder you want to put a background image.
- make sure you can view hidden files (tools>folder options>view>show hidden files and folders).
- open the file "desktop.ini" in note pad
- delete the existing code and paste this code:
iconarea_image=.\image.jpg
iconarea_text=0x00FFFFFF
5. Edit the last line of code (IconArea_Image=C:\My Folder Background.jpg) to the path of your picture, save the file and close it. Refresh your folder and it should have the new background.