Change the desktop background in code

I'd like to write a program that would run at startup, and would randomly choose a desktop background from a folder of images, and make Windows use that image. Any ideas how to change the background in code?

the wallpaper appears to be stored in the registry here: HKEY_USERS\S-1-5-21-682003330-1417001333-839522115-1004\Control Panel\Desktop

on my machine.

*EDIT*
although it looks like SetSystemParametersInfo() combined with SPI_SETDESKWALLPAPER might be a safer bet

although if you're going for a registry approach, HKEY_CURRENT_USER\Control Panel\Desktop\wallpaper looks better than my first registry entry

This C#/VB example should be simple enough to convert.

http://blogs.msdn.com/coding4fun/archive/2006/10/31/912569.aspx

Here's a little app that will change the background regularly:

Framework brl.linkedlist
Import brl.filesystem
Import brl.retro
Import leadwerks.appsettings

Const SPI_SETDESKWALLPAPER=20

Extern "win32"
	Function SystemParametersInfoA:Int(uiAction,uiParam,pvParam$z,fWinIni)
EndExtern

bgpath$=AppDir
LoadAppSettings()
bgpath=AppSetting("wallpaperdir",bgpath)

Local list:TList=New TList

d=ReadDir(bgpath)
If Not d End
Repeat
	file$=NextFile(d)
	If file="" Exit
	If Lower(ExtractExt(file))="bmp"
		count:+1
		list.addlast bgpath+"/"+file
	EndIf
Forever
CloseDir d

SeedRnd MilliSecs()
Repeat

	Delay 1000*60*5

	bgfile$=String(list.valueatindex(Rand(0,count-1)))
	SystemParametersInfoA SPI_SETDESKWALLPAPER,0,bgfile,0

Forever
End

is leadwerks.appsettings available somewhere ? I'd a quick look at your website but it wasn't obvious...