public class WatermarkHelper

    {

        string _waterImgPath;

        BitmapSource _waterPic;

        string _prefix = null;



        // constructors

        public WatermarkHelper(string waterImgFilePath, string prefix = null)

        {

            this._waterImgPath = waterImgFilePath;

            this._waterPic = new BitmapImage(new Uri(this._waterImgPath));

            if (prefix == null)

                prefix = "";

            this._prefix = prefix;

            // this._result = false;

        }





        // public members

        public void AddWatermark_SaveToDir(string inputFilePath, string outputDir)

        {

            if (!Directory.Exists(outputDir))

                Directory.CreateDirectory(outputDir);

            string output_filepath = Path.Combine(

                outputDir,

                string.Format("{0}{1}", this._prefix, Path.GetFileName(inputFilePath))

                );  // <-- use Path.Combine to prevent potential problems



            //  process

            Process(inputFilePath, output_filepath);

        }





        public void AddWatermark_SaveToFile(string inputFilePath, string output_filepath) // <-- you see what i mean when i say 'flexibility'

        {

            // create directory if it doesn't exist yet

            string output_dir = Path.GetDirectoryName(output_filepath);

            if (!Directory.Exists(output_dir))

                Directory.CreateDirectory(output_dir);



            //  process

            Process(inputFilePath, output_filepath);

        }





        // internal logic

        bool Process(string input_filepath, string output_filepath) // <-- let upper logic determine the output filename, these will provide flexibility

        {

            // load source image

            // BitmapSource bitmap = new BitmapImage(new Uri(input_filepath));

            BitmapImage bitmap = new BitmapImage();

            bitmap.BeginInit();

            bitmap.UriSource = new Uri(input_filepath);

            bitmap.CacheOption = BitmapCacheOption.OnLoad;

            bitmap.EndInit();



            // create render bitmap

            var rtbitmap = new RenderTargetBitmap(bitmap.PixelWidth,

                bitmap.PixelHeight,

                bitmap.DpiX,

                bitmap.DpiY,

                PixelFormats.Default);

            // draw watermark

            var drawingVisual = new DrawingVisual();

            using (var dc = drawingVisual.RenderOpen())

            {

                // draw source image

                dc.DrawImage(bitmap, new Rect(0, 0, bitmap.Width, bitmap.Height));

                // determine the render size of the watermark

                double hs = bitmap.Height * 0.3 / this._waterPic.Height;

                double ws = bitmap.Width * 0.3 / this._waterPic.Width;

                double scale = hs > ws ? ws : hs;

                if (bitmap.Height / bitmap.Width > 5)

                {

                    scale = bitmap.Width * 0.8 / this._waterPic.Width;

                }

                else if (bitmap.Width / bitmap.Height > 5)

                {

                    scale = bitmap.Height * 0.8 / this._waterPic.Height;

                }

                double Wstart = bitmap.Width - this._waterPic.Width * scale - 20 < 0 ? 0 : bitmap.Width - this._waterPic.Width * scale - 20;

                double Hstart = bitmap.Height - this._waterPic.Height * scale;

                // draw water make

                dc.DrawImage(this._waterPic, new Rect(Wstart, Hstart, this._waterPic.Width * scale, this._waterPic.Height * scale));

            }

            rtbitmap.Render(drawingVisual);

            var bitmapEncoder = new PngBitmapEncoder();

            bitmapEncoder.Frames.Add(BitmapFrame.Create(rtbitmap));



            // save image

            if (File.Exists(output_filepath))

                File.Delete(output_filepath);



            using (FileStream file = new FileStream(output_filepath, FileMode.Create))

                bitmapEncoder.Save(file);



            // return

            return true;

        }

    }

 #region 图片加上水印的操作



        /// <summary>

        /// 向图片上写文字再输出

        /// </summary>

        /// <param name="img"></param>

        /// <param name="text"></param>

        /// <returns></returns>

        public static Image WriteString(Image img, string text)

        {

            Bitmap bmap = new Bitmap(img);

            Graphics g = Graphics.FromImage(bmap);

            Font font = new Font("楷体", 15);

            PointF pf = new PointF();//((float)(img.Width/2-2.5),img.Height/2-2.5);

            pf.X = 0;

            pf.Y = 0;



            g.DrawString(text, font, Brushes.Gold, pf);

            g.Dispose();



            return bmap;

        }

        /// <summary>

        /// 将图片加载水印图片

        /// </summary>

        /// <param name="markImg"></param>

        /// <param name="fromImg"></param>

        /// <returns></returns>

        public static Image WriteImg(Image markImg, Image fromImg)

        {

            Bitmap b = new Bitmap(fromImg);

            Graphics g = Graphics.FromImage(b);

            g.DrawImage(markImg, 0, 0, markImg.Width, markImg.Height);

            g.Dispose();

            return b;

        }



        #endregion