[opardor]

En lugar de usar el TImage te recomiendo uses TBitmap y luego se lo asignes al imgEnviar..

procedure TExplorer.Timer1Timer(Sender: TObject);
var
  DeskTop : TBitmap ;
begin
  DeskTop := TBitmap.Create ;
  try
	with DeskTop do begin
	  Handle := GetWindowDC (GetDesktopWindow) ;
	  Width :=  GetDeviceCaps( handle, HORZRES );
	  Height := GetDeviceCaps( handle, VERTRES );
	  BitBlt(Canvas.Handle,0,0,Width, Height,handle,0,0,SRCCOPY);
	  imgEnviar.Picture.Bitmap := Desktop;
   end;
 finally
   DeskTop.Free;
 end
end;

Espero te sirva!!