procedure TForm1.ScreenCap(LeftPos, TopPos, RightPos, BottomPos: Integer);
var
RectWidth, RectHeight: Integer;
SourceDC, DestDC, Bhandle: Integer;
Bitmap: TBitmap;
begin
RectWidth := RightPos - LeftPos;
RectHeight := BottomPos - TopPos;
SourceDC := CreateDC('DISPLAY', '', '', nil);
DestDC := CreateCompatibleDC(SourceDC);
Bhandle := CreateCompatibleBitmap(SourceDC, RectWidth, RectHeight);
SelectObject(DestDC, Bhandle);
BitBlt(DestDC, 0, 0, RectWidth, RectHeight, SourceDC, LeftPos, TopPos, SRCCOPY);
Bitmap := TBitmap.Create;
Bitmap.Handle := Bhandle;
Image1.Picture.Bitmap := Bitmap;
Bitmap.SaveToFile('test.bmp');
Bitmap.Free;
DeleteDC(DestDC);
ReleaseDC(Bhandle, SourceDC);
end;