在C#中添加不可见的图像水印？

using System;
using System.Drawing;
using System.Drawing.Imaging;

public class InvisibleWatermark
{
    public static void AddInvisibleWatermark(string inputPath, string outputPath, string watermarkText)
    {
        using (Bitmap bitmap = new Bitmap(inputPath))
        {
            using (BitmapData bitmapData = bitmap.LockBits(new Rectangle(0, 0, bitmap.Width, bitmap.Height), ImageLockMode.ReadWrite, bitmap.PixelFormat))
            {
                int bytesPerPixel = Image.GetPixelFormatSize(bitmap.PixelFormat) / 8;
                int byteCount = bitmapData.Stride * bitmap.Height;
                byte[] pixelData = new byte[byteCount];
                IntPtr scan0 = bitmapData.Scan0;
                System.Runtime.InteropServices.Marshal.Copy(scan0, pixelData, 0, byteCount);

                for (int i = 0; i< byteCount; i += bytesPerPixel)
                {
                    // 在这里添加你的水印数据
                    pixelData[i] = (byte)watermarkText[i % watermarkText.Length];
                }

                System.Runtime.InteropServices.Marshal.Copy(pixelData, 0, scan0, byteCount);
                bitmap.UnlockBits(bitmapData);
                bitmap.Save(outputPath, ImageFormat.Jpeg);
            }
        }
    }
}