var DC:HDC;
      bm:TBitMap;
...
bm:=TBitMap.Create;
DC:=GetDC(0);   // получишь DC экрана
// при сохранении куска раб. стола
...
bm.width:=w;
bm.height:=h;    // ширина и высота копируемой области
bitblt(bm.canvas.handle,0,0,w-1,h-1,DC,x,y,SRCCOPY); // копировать в BM кусок из DC WxH
...
//При загрузке
bitblt(DC,x,y,w-1,h-1,bm.canvas.handle,0,0,SRCCOPY) // копировать на экран

windows.MoveToEx(DC,x,y,nil);
windows.LineTo(DC,x+w-1,y+h-1);

procedure TForm2.FormMouseDown(Sender: TObject; Button: TMouseButton;
       Shift: TShiftState; X, Y: Integer);
begin
pos1 := Point(X, Y);
risuem := true;
Form2.AlphaBlendValue := 80;
end;

procedure TForm2.FormMouseUp(Sender: TObject; Button: TMouseButton;
       Shift: TShiftState; X, Y: Integer);
       var
ScreenDC:HDC;
Canvas:TCanvas;
myjpg:  TJPEGImage;
Image: TImage;
       begin
pos2 := Point(X, Y);
risuem := false;
Form2.AlphaBlendValue := 1;

Image:=TImage.Create(nil);
myjpg:= TJPEGImage.Create;
ScreenDC := GetDC(0);
Canvas:=TCanvas.Create();
Canvas.Handle:=ScreenDC;
Image.Width := pos2.X - pos1.X;
Image.Height := pos2.y - pos1.y;
Image.Canvas.CopyRect(Rect(0,0,Image.Width,Image.Height), Canvas, Rect(pos1, pos2));
ReleaseDC(0,ScreenDC);
myjpg.Assign(Image.Picture.Bitmap);
myjpg.compressionquality:=100;
myjpg.compress;
myjpg.SaveToFile('prob.jpg');
Image.Free;
Canvas.Free;
       close;
end;

procedure TForm2.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
       Y: Integer);
begin
       if risuem = true then
       begin
         Form2.Canvas.Pen.Color := clNone;
         Form2.Canvas.Brush.Color := clBtnFace;
         Form2.Canvas.Rectangle(0,0,Form2.Width, Form2.Height);
         Form2.Canvas.Pen.Color := clred;
         Form2.Canvas.Brush.Color := clBlack;
         Form2.Canvas.Rectangle(Classes.Rect(pos1, Point(x, y)));
         pos3 := Point(X, Y);
       end;
end;

procedure TForm2.FormCreate(Sender: TObject);
begin
       Form2.Canvas.Pen.Color := clred;
       Form2.Canvas.Brush.Color := clBlack;
end;

end.

procedure TForm1.Button1Click(Sender: TObject);
var
foo: TPoint;
begin
GetCursorPos(foo);
Edit1.Text:=(IntToStr(foo.Y));
Edit2.Text:=(IntToStr( foo.X));
end;