Example Opera Neon window background like - Enjoy ;-)

var
  FormRatio,PictureRatio:real;
  Picture:TPicture;

procedure Form1_OnResize (Sender: TObject);
var
  width,
  height:integer;
begin
  if PictureRatio>0 then
  begin
    FormRatio:=Form1.Width/Form1.Height;
    if (PictureRatio>FormRatio) then
    begin            
      width:=Round(Form1.Height*PictureRatio);
      Form1.Image1.Width:=width;
      Form1.Image1.left:=Round((Form1.Width-width)/2);
    end;

    if (PictureRatio<FormRatio) then
    begin
      height:=Round(Form1.Width/PictureRatio);
      Form1.Image1.Height:=height;
      Form1.Image1.top:=Round((Form1.Height-height)/2);
    end;
  end;
end;

procedure Form1_OnClose (Sender: TObject; Action: string);
begin
  Picture.Free;
end;

procedure Form1_OnShow (Sender: TObject; Action: string);
begin
  Picture:=TPicture.Create();
  Picture.LoadFromFile(GetBackgroundImage());
  PictureRatio:=Picture.Width/Picture.Height;
  Form1.Image1.Picture:=Picture;
end;
                
function GetBackgroundImage(): string;
var
  Registry: TRegistry;
begin
  Registry := TRegistry.Create();
  try
    Registry.Access := KEY_READ;
    Registry.RootKey := HKEY_CURRENT_USER;
    Registry.OpenKey('Control Panel\Desktop', False);
    Result := Registry.ReadString('Wallpaper');
  finally
    Registry.Free;
  end;
end;

begin
  Form1.mniFile.Visible := False;
  Form1.mniOptions.Visible := False;
  Form1.mniSettings.Visible := False;
  Form1.mniReport.Visible := False;
  Form1.mniAbout.Visible := False;
end.