将矩形保存到位图图片

Question

我正在尝试在图像的位图上的特定区域周围绘制蓝​​色矩形。但出现错误EventArg没有图形

private void SaveBtn_Click(object sender, EventArgs e)
    {
        // asking the user for the location and name the user wants for this file
        SaveFileDialog dialog = new SaveFileDialog();
        // getting the file type options 
        dialog.Filter = "Bitmap Image (.bmp)|*.bmp|Gif Image (.gif)|*.gif |JPEG Image (.jpeg)|*.jpeg |Png Image (.png)|*.png";


        // getting the currecntFrame from the Video Source Player control
        Bitmap currentFrame = videoSourcePlayer.GetCurrentVideoFrame();


        // Create graphics object for alteration.
        Graphics newGraphics = Graphics.FromImage(currentFrame);

        // Alter image.
        newGraphics.DrawRectangle(Pens.AliceBlue, _stIR.X, _stIR.Y, _endIR.X - _stIR.X, _endIR.Y - _stIR.Y);

        // Draw image to screen.
        e.Graphics.DrawImage(currentFrame, new PointF(0.0F, 0.0F));

        // Dispose of graphics object.
        newGraphics.Dispose();


        // if the user click ok 
        if (dialog.ShowDialog() == DialogResult.OK)
        {
            // save the pictures 
            currentFrame.Save(dialog.FileName, ImageFormat.Png);
        }
    }

我希望能够在我拥有的图像上方的某个区域周围保存一个蓝色矩形。因此，它就是图像和图像内部某处周围的蓝色矩形。