Your shell can display specific desktop wallpaper by retrieving the current wallpaper registry values from the HKEY_CURRENT_USER\ControlPanel\Desktop registry key.

To specify the name of the wallpaper bitmap to retrieve, set the HKEY_CURRENT_USER\ControlPanel\Desktop\Wallpaper registry value to a string that is the path to the bitmap. The following registry key example shows how to set this registry value.

"Wallpaper": REG_SZ

To specify whether to tile the wallpaper bitmap, set the HKEY_CURRENT_USER\ControlPanel\Desktop\Tile registry value. Set this registry value to 1 to display the wallpaper bitmap as repeating tiles, set to 0 to display the bitmap normally. The following registry key example shows how to set this registry value.

"Tile": REG_DWORD

Finally, call PostMessage to post the message to all top-level windows in the system, including disabled or invisible unowned windows, overlapped windows, and pop-up windows. This call is shown in the following code snippet.

PostMessage(HWND_BROADCAST, WM_SETTINGCHANGE, SPI_SETDESKWALLPAPER, 0);