Title: Change the wallpaper in Delphi
Use SystemParametersInfo procedure with SPI_SETDESCKWALLPAPER value.
procedure TForm1.Button1Click(Sender: TObject);
var
St: array[0..100] of Char;
begin
St:='C:\Windows\MyWallPaper.bmp';
SystemParametersInfo(SPI_SETDESKWALLPAPER, 0, @St, SPIF_SENDCHANGE);
end;