如何防止将图像拖放到表单之外？

Question

我正在制作国际象棋棋盘，但我不想允许用户将国际象棋棋子（图像）拖放到表单之外。

当前代码：

private void PictureBox_MouseDown(object sender, MouseEventArgs e)
    {
        PictureBox pb = (PictureBox)sender;
        pb.DoDragDrop(pb.Image, DragDropEffects.Copy);
    }
private void PictureBox_DragEnter(object sender, DragEventArgs e)
    {
        PictureBox pb = (PictureBox)sender;
        pb.Image = DragDropPreview(e);
    }
private void PictureBox_DragDrop(object sender, DragEventArgs e)
    {
        PictureBox pb = (PictureBox)sender;
        pb.Image = (Bitmap)e.Data.GetData(DataFormats.Bitmap);
    }
private void PictureBox_DragLeave(object sender, EventArgs e)
    {
        PictureBox pb = (PictureBox)sender;
        pb.Image = null;
    }

是否可以防止用户将图像拖出表格？

 private void frmChessBoard_DragLeave(object sender, EventArgs e)
    {
        // stop the Drag & Drop action
    }

还是有一种不允许将图像拖放到表格之外的方法？ 我不知道是否可以触发表单之外的事件。