C# How can I watermark a jpeg image?

Using C# how would I watermark an jpeg image that I'm reading into a memory stream and saving to a byte array?

using (MemoryStream imageStream = new MemoryStream())
{
      pbPreview.Image.Save(imageStr开发者_JAVA技巧eam, ImageFormat.Jpeg);
      photoBytes = imageStream.ToArray();
}

Thank you

Please take a look: Watermark Creator and Creating a Watermarked Photograph with GDI+ for .NET

A more detailed explanation here: Build a simple watermarking utility in C#