Двигаем крестик для показа значений X/Y

// TPanel, TImage e TLabel components
// Insert Image into Panel...
 
private
   BmpH, BmpV : TBitmap;
   OldX, OldY: Integer;
end;
 
var
  RectSaved : boolean = false;
 
procedure TFormMain.FormCreate(Sender: TObject);
begin
  PanelImage.DoubleBuffered := true; // This prevents that the image is blinking
  LabelHint.Transparent := true;
  LabelHint.Font.Color := clNave;
end;
 
procedure TFormMain.FormMouseMove(Sender: TObject; Shift: TShiftState; X,
  Y: Integer);
begin
  Cross(X, Y);
end;
 
procedure TFormMain.Cross(X, Y: Integer);
begin
  Image.Canvas.Pen.Color := clBlack;
  // Restore last image to erase line
  if RectSaved then
  begin
    Image.Canvas.CopyRect(Rect(OldX - 5, 0, OldX + 5, BmpV.Height),
    BmpV.Canvas, Rect(0,0,BmpV.Width,BmpV.Height));
    Image.Canvas.CopyRect(Rect(0, OldY - 5, BmpH.Width, OldY + 5),
    BmpH.Canvas, Rect(0,0,BmpH.Width,BmpH.Height));
    BmpH.Free;
    BmpV.Free;
  end;
  // Now save the image at new position for each line
  // horizontal line
  BmpH := TBitmap.Create;
  BmpH.Width := Image.Width;
  BmpH.Height := 10;
  BmpH.Canvas.CopyRect(Rect(0,0,BmpH.Width,BmpH.Height),
  Image.Canvas,Rect(0, Y - 5, BmpH.Width, Y + 5));
  // Vertical line
  BmpV := TBitmap.Create;
  BmpV.Width := 10;
  BmpV.Height := Image.Height;
  BmpV.Canvas.CopyRect(Rect(0,0,BmpV.Width,BmpV.Height),
                 Image.Canvas,Rect(X - 5, 0, X + 5, BmpV.Height));
 
  // Now draw the current position
  Image.Canvas.MoveTo(0, Y);
  Image.Canvas.LineTo(Image.Width, Y);
  Image.Canvas.MoveTo(X, 0);
  Image.Canvas.LineTo(X, Image.Height);
 
  RectSaved := true;
  OldX := X;
  OldY := Y;
 
  LabelHint.Left := X + 36;
  LabelHint.Top := Y - 15;
  LabelHint.Caption := '(X:' + IntToStr(X) + ' x Y:' + IntToStr(Y) +')';
end;

Взято с сайта https://www.swissdelphicenter.ch/en/tipsindex.php