//using System.Drawing;
//using System.IO;
//using System.Drawing.Imaging;

private void AddTextToImg(string fileName,string text)
{
   if(!File.Exists(MapPath(fileName)))
   {
       throw new FileNotFoundException("The file don't exist!");
   }
   
   if( text == string.Empty )
   {
       return;
   }
   //还需要判断文件类型是否为图像类型，这里就不赘述了

   System.Drawing.Image image = System.Drawing.Image.FromFile(MapPath(fileName));
   Bitmap bitmap = new Bitmap(image,image.Width,image.Height);
   Graphics g = Graphics.FromImage(bitmap);

   float fontSize = 12.0f;    //字体大小
   float textWidth = text.Length*fontSize;  //文本的长度
   //下面定义一个矩形区域，以后在这个矩形里画上白底黑字
   float rectX = 0;        
   float rectY = 0;
   float rectWidth = text.Length*(fontSize+8);
   float rectHeight = fontSize+8;
   //声明矩形域
   RectangleF textArea = new RectangleF(rectX,rectY,rectWidth,rectHeight);

   Font font = new Font("宋体",fontSize);   //定义字体
   Brush whiteBrush = new SolidBrush(Color.White);   //白笔刷，画文字用
   Brush blackBrush = new SolidBrush(Color.Black);   //黑笔刷，画背景用

   g.FillRectangle(blackBrush,rectX,rectY,rectWidth,rectHeight);   

   g.DrawString(text,font,whiteBrush,textArea);
   MemoryStream ms = new MemoryStream( );
   //保存为Jpg类型
   bitmap.Save(ms,ImageFormat.Jpeg);

   //输出处理后的图像，这里为了演示方便，我将图片显示在页面中了
   Response.Clear();
   Response.ContentType = "image/jpeg";
   Response.BinaryWrite( ms.ToArray() );

   g.Dispose();
   bitmap.Dispose();
   image.Dispose();
}

//using System; 
//using System.Web; 
//using System.Drawing; 
//using System.Drawing.Drawing2D; 
//using System.Drawing.Imaging; 
//using System.IO; 
//using System.Reflection; 

/// <summary> 
/// 给图片上水印 
/// </summary> 
/// <param name="filePath">原图片地址</param> 
/// <param name="waterFile">水印图片地址</param> 
public void MarkWater(string filePath,string waterFile) 
{ 
    //GIF不水印 
    int i = filePath.LastIndexOf("."); 
    string ex = filePath.Substring(i,filePath.Length - i); 
    if(string.Compare(ex,".gif",true) == 0) 
    { 
        return; 
    } 

    string ModifyImagePath = BasePath + filePath;//修改的图像路径 
    int lucencyPercent=25; 
    Image modifyImage=null; 
    Image drawedImage=null; 
    Graphics g=null; 
    try 
    { 
        //建立图形对象 
        modifyImage=Image.FromFile(ModifyImagePath,true); 
        drawedImage=Image.FromFile(BasePath + waterFile,true); 
        g=Graphics.FromImage(modifyImage); 
        //获取要绘制图形坐标 
        int x=modifyImage.Width-drawedImage.Width; 
        int y=modifyImage.Height-drawedImage.Height; 
        //设置颜色矩阵 
        float[][] matrixItems ={ 
            new float[] {1, 0, 0, 0, 0}, 
            new float[] {0, 1, 0, 0, 0}, 
            new float[] {0, 0, 1, 0, 0}, 
            new float[] {0, 0, 0, (float)lucencyPercent/100f, 0}, 
            new float[] {0, 0, 0, 0, 1}}; 

        ColorMatrix colorMatrix = new ColorMatrix(matrixItems); 
        ImageAttributes imgAttr=new ImageAttributes(); 
        imgAttr.SetColorMatrix(colorMatrix,ColorMatrixFlag.Default,ColorAdjustType.Bitmap); 
        //绘制阴影图像 
        g.DrawImage(drawedImage,new Rectangle(x,y,drawedImage.Width,drawedImage.Height),10,10,drawedImage.Width,drawedImage.Height,GraphicsUnit.Pixel,imgAttr); 
        //保存文件 
        string[] allowImageType={".jpg",".gif",".png",".bmp",".tiff",".wmf",".ico"}; 
        FileInfo fi=new FileInfo(ModifyImagePath); 
        ImageFormat imageType=ImageFormat.Gif; 
        switch(fi.Extension.ToLower()) 
        { 
            case ".jpg": imageType=ImageFormat.Jpeg; break; 
            case ".gif": imageType=ImageFormat.Gif; break; 
            case ".png": imageType=ImageFormat.Png; break; 
            case ".bmp": imageType=ImageFormat.Bmp; break; 
            case ".tif": imageType=ImageFormat.Tiff; break; 
            case ".wmf": imageType=ImageFormat.Wmf; break; 
            case ".ico": imageType=ImageFormat.Icon; break; 
            default: break; 
        } 
        MemoryStream ms=new MemoryStream(); 
        modifyImage.Save(ms,imageType); 
        byte[] imgData=ms.ToArray(); 
        modifyImage.Dispose(); 
        drawedImage.Dispose(); 
        g.Dispose(); 
        FileStream fs=null; 
        File.Delete(ModifyImagePath); 
        fs=new FileStream(ModifyImagePath,FileMode.Create,FileAccess.Write); 
        if(fs!=null) 
        { 
            fs.Write(imgData,0,imgData.Length); 
            fs.Close(); 
        } 
    } 
    finally 
    { 
        try 
        { 
            drawedImage.Dispose(); 
            modifyImage.Dispose(); 
            g.Dispose(); 
        } 
        catch
        {
        } 
   } 
} 

<summary>
   /// 添加图片水印
   /// </summary>
   /// <param name="path">原图片绝对地址</param>
   /// <param name="Ext">文件后缀</param>
   public static string addWaterMark(string path,string fileExt)
   {
    System.Drawing.Image image = System.Drawing.Image.FromFile(path);
    Bitmap b = new Bitmap(image.Width, image.Height,System.Drawing.Imaging.PixelFormat.Format24bppRgb);
    Graphics g = Graphics.FromImage(b);
    g.Clear(Color.White);
    g.DrawImage(image, 0, 0, image.Width, image.Height);

    Image watermark = new Bitmap(ConfigurationSettings.AppSettings["PersonalPath"] + @"images/logo.jpg");

    System.Drawing.Imaging.ImageAttributes imageAttributes = new System.Drawing.Imaging.ImageAttributes();
    System.Drawing.Imaging.ColorMap colorMap = new System.Drawing.Imaging.ColorMap();
    colorMap.OldColor = Color.FromArgb(255, 0, 255, 0);
    colorMap.NewColor = Color.FromArgb(0, 0, 0, 0);
    System.Drawing.Imaging.ColorMap[] remapTable = {colorMap};
    imageAttributes.SetRemapTable(remapTable, System.Drawing.Imaging.ColorAdjustType.Bitmap);
    float[][] colorMatrixElements = {
             new float[] {1.0f, 0.0f, 0.0f, 0.0f, 0.0f},
             new float[] {0.0f, 1.0f, 0.0f, 0.0f, 0.0f},
             new float[] {0.0f, 0.0f, 1.0f, 0.0f, 0.0f},
             new float[] {0.0f, 0.0f, 0.0f, 0.3f, 0.0f},
             new float[] {0.0f, 0.0f, 0.0f, 0.0f, 1.0f}
            };
    System.Drawing.Imaging.ColorMatrix colorMatrix = new System.Drawing.Imaging.ColorMatrix(colorMatrixElements);
    imageAttributes.SetColorMatrix(colorMatrix, System.Drawing.Imaging.ColorMatrixFlag.Default, System.Drawing.Imaging.ColorAdjustType.Bitmap);
    int xpos = 0;
    int ypos = 0;
   
    xpos = ((image.Width - watermark.Width) - 10);
    ypos = image.Height - watermark.Height - 10;

    g.DrawImage(watermark, new Rectangle(xpos, ypos, watermark.Width, watermark.Height), 0, 0, watermark.Width, watermark.Height, GraphicsUnit.Pixel, imageAttributes);

    watermark.Dispose();
    imageAttributes.Dispose();


    //保存加水印过后的图片,删除原始图片
    Random ro=new Random((int)DateTime.Now.Ticks);
    string temppath = System.DateTime.Now.ToString("yyyy") + "//" + System.DateTime.Now.ToString("MMdd");
    string fileName = temppath + "//" + DateTime.Now.ToString("yyyyMMddHHmmss") + ro.Next(10000) + fileExt;
    string filepath = Functions.GetUserFactPath(User.GetUserFromSession().Adddate,User.GetUserFromSession().UserId) + "3//";
   

    b.Save(filepath + fileName);
    b.Dispose();
    image.Dispose();
    if(File.Exists(path))
    {
     File.Delete(path);
    }

    return fileName;
   }

/*
 * Class:WaterImage
 * Use for add a water Image to the picture both words and image
 * 2007.07.23   create the file
 *
 * http://www.freeatom.com/  欢迎您的来访
 * 
 * 使用说明：
 * 　建议先定义一个WaterImage实例
 * 　然后利用实例的属性，去匹配需要进行操作的参数
 * 　然后定义一个WaterImageManage实例
 * 　利用WaterImageManage实例进行DrawImage（），印图片水印
 * 　DrawWords（）印文字水印
 * 
-*/

using System;
using System.Drawing;
using System.Drawing.Imaging;
using System.Drawing.Drawing2D;
using System.IO;
/// <summary>
/// 图片位置
/// </summary>
public enum ImagePosition
{
    LeftTop,        //左上
    LeftBottom,    //左下
    RightTop,       //右上
    RigthBottom,  //右下
    TopMiddle,     //顶部居中
    BottomMiddle, //底部居中
    Center           //中心
}

/// <summary>
/// 水印图片的操作管理 Design by Gary Gong From Demetersoft.com
/// </summary>
public class WaterImageManage
{
    /// <summary>
    /// 生成一个新的水印图片制作实例
    /// </summary>
    public WaterImageManage ()
    {
        //
        // TODO: Add constructor logic here
        //
    }

    /// <summary>
    /// 添加图片水印
    /// </summary>
    /// <param name="sourcePicture">源图片文件名</param>
    /// <param name="waterImage">水印图片文件名</param>
    /// <param name="alpha">透明度(0.1-1.0数值越小透明度越高)</param>
    /// <param name="position">位置</param>
    /// <param name="PicturePath" >图片的路径</param>
    /// <returns>返回生成于指定文件夹下的水印文件名</returns>
    public string  DrawImage(string sourcePicture,
                                      string waterImage,
                                      float alpha,
                                      ImagePosition position,
                                      string PicturePath )
    {
        //
        // 判断参数是否有效
        //
        if (sourcePicture == string.Empty || waterImage == string.Empty || alpha == 0.0 || PicturePath == string.Empty)
        {
            return sourcePicture;
        }

        //
        // 源图片，水印图片全路径
        //
        string sourcePictureName = PicturePath + sourcePicture;
        string waterPictureName = PicturePath + waterImage;
        string fileSourceExtension = System.IO.Path.GetExtension(sourcePictureName).ToLower();
        string fileWaterExtension = System.IO.Path.GetExtension(waterPictureName).ToLower();
        //
        // 判断文件是否存在,以及类型是否正确
        //
        if (System.IO.File.Exists(sourcePictureName) == false || 
            System.IO.File.Exists(waterPictureName) == false ||(
            fileSourceExtension != ".gif" &&
            fileSourceExtension != ".jpg" &&
            fileSourceExtension != ".png") || (
            fileWaterExtension != ".gif" &&
            fileWaterExtension != ".jpg" &&
            fileWaterExtension != ".png")
            )
        {
            return sourcePicture;
        }

        //
        // 目标图片名称及全路径
        //
        string targetImage = sourcePictureName.Replace ( System.IO.Path.GetExtension(sourcePictureName),"") + "_1101.jpg";

        //
        // 将需要加上水印的图片装载到Image对象中
        //
        Image imgPhoto = Image.FromFile(sourcePictureName);
        //
        // 确定其长宽
        //
        int phWidth = imgPhoto.Width;
        int phHeight = imgPhoto.Height;

        //
        // 封装 GDI+ 位图，此位图由图形图像及其属性的像素数据组成。
        //
        Bitmap bmPhoto = new Bitmap(phWidth, phHeight, PixelFormat.Format24bppRgb);

        //
        // 设定分辨率
        // 
        bmPhoto.SetResolution(imgPhoto.HorizontalResolution, imgPhoto.VerticalResolution);

        //
        // 定义一个绘图画面用来装载位图
        //
        Graphics grPhoto = Graphics.FromImage(bmPhoto);

        //
        //同样，由于水印是图片，我们也需要定义一个Image来装载它
        //
        Image imgWatermark = new Bitmap(waterPictureName);
        
        //
        // 获取水印图片的高度和宽度
        //
        int wmWidth = imgWatermark.Width;
        int wmHeight = imgWatermark.Height;

        //SmoothingMode：指定是否将平滑处理（消除锯齿）应用于直线、曲线和已填充区域的边缘。
        // 成员名称   说明 
        // AntiAlias      指定消除锯齿的呈现。  
        // Default        指定不消除锯齿。  
        // HighQuality  指定高质量、低速度呈现。  
        // HighSpeed   指定高速度、低质量呈现。  
        // Invalid        指定一个无效模式。  
        // None          指定不消除锯齿。 
        grPhoto.SmoothingMode = SmoothingMode.AntiAlias;

        //
        // 第一次描绘，将我们的底图描绘在绘图画面上
        //
        grPhoto.DrawImage(imgPhoto,                                          
                                    new Rectangle(0, 0, phWidth, phHeight), 
                                    0,     
                                    0,       
                                    phWidth,   
                                    phHeight,      
                                    GraphicsUnit.Pixel);    

        //
        // 与底图一样，我们需要一个位图来装载水印图片。并设定其分辨率
        //
        Bitmap bmWatermark = new Bitmap(bmPhoto);
        bmWatermark.SetResolution(imgPhoto.HorizontalResolution, imgPhoto.VerticalResolution);
        
        //
        // 继续，将水印图片装载到一个绘图画面grWatermark
        //
        Graphics grWatermark = Graphics.FromImage(bmWatermark);

        //
        //ImageAttributes 对象包含有关在呈现时如何操作位图和图元文件颜色的信息。
        //       
        ImageAttributes imageAttributes = new ImageAttributes();

        //
        //Colormap: 定义转换颜色的映射
        //
        ColorMap colorMap = new ColorMap();

        //
        //我的水印图被定义成拥有绿色背景色的图片被替换成透明
        //
        colorMap.OldColor = Color.FromArgb(255, 0, 255, 0);
        colorMap.NewColor = Color.FromArgb(0, 0, 0, 0);

        ColorMap[] remapTable = { colorMap };

        imageAttributes.SetRemapTable(remapTable, ColorAdjustType.Bitmap);

        float[][] colorMatrixElements = { 
           new float[] {1.0f,  0.0f,  0.0f,  0.0f, 0.0f}, // red红色
           new float[] {0.0f,  1.0f,  0.0f,  0.0f, 0.0f}, //green绿色
           new float[] {0.0f,  0.0f,  1.0f,  0.0f, 0.0f}, //blue蓝色       
           new float[] {0.0f,  0.0f,  0.0f,  alpha, 0.0f}, //透明度     
           new float[] {0.0f,  0.0f,  0.0f,  0.0f, 1.0f}};//

        //  ColorMatrix:定义包含 RGBA 空间坐标的 5 x 5 矩阵。
        //  ImageAttributes 类的若干方法通过使用颜色矩阵调整图像颜色。
        ColorMatrix wmColorMatrix = new ColorMatrix(colorMatrixElements);


        imageAttributes.SetColorMatrix(wmColorMatrix, ColorMatrixFlag.Default,
         ColorAdjustType.Bitmap);

        //
        //上面设置完颜色，下面开始设置位置
        //
        int xPosOfWm;
        int yPosOfWm; 

        switch (position)
        {
            case ImagePosition .BottomMiddle :
                xPosOfWm = (phWidth-wmWidth ) / 2 ;
                yPosOfWm = phHeight- wmHeight -10;
                break ;
            case ImagePosition .Center :
                xPosOfWm = (phWidth - wmWidth) / 2;
                yPosOfWm = (phHeight-wmHeight ) / 2;
                break ;
            case ImagePosition .LeftBottom :
                xPosOfWm = 10;
                yPosOfWm = phHeight - wmHeight - 10;
                break ;
            case ImagePosition .LeftTop :
                xPosOfWm = 10;
                yPosOfWm = 10;
                break;
            case ImagePosition .RightTop :
                xPosOfWm = phWidth - wmWidth - 10;
                yPosOfWm = 10;
                break ;
            case ImagePosition .RigthBottom :
                xPosOfWm = phWidth - wmWidth - 10;
                yPosOfWm = phHeight - wmHeight - 10;
                break ;
            case ImagePosition.TopMiddle :
                xPosOfWm = (phWidth - wmWidth) / 2;
                yPosOfWm = 10;
                break ;
            default:
                xPosOfWm = 10;
                yPosOfWm = phHeight - wmHeight - 10;
                break;
        }

        //
        // 第二次绘图，把水印印上去
        //
        grWatermark.DrawImage(imgWatermark,
         new Rectangle(xPosOfWm,
                             yPosOfWm,
                             wmWidth,
                             wmHeight), 
                             0,              
                             0,          
                             wmWidth,  
                             wmHeight,   
                             GraphicsUnit.Pixel,  
                             imageAttributes); 

       
        imgPhoto = bmWatermark;
        grPhoto.Dispose();
        grWatermark.Dispose();

        //
        // 保存文件到服务器的文件夹里面
        //
        imgPhoto.Save(targetImage, ImageFormat.Jpeg);
        imgPhoto.Dispose();
        imgWatermark.Dispose();
        return targetImage.Replace (PicturePath,"");
    }

    /// <summary>
    /// 在图片上添加水印文字
    /// </summary>
    /// <param name="sourcePicture">源图片文件</param>
    /// <param name="waterWords">需要添加到图片上的文字</param>
    /// <param name="alpha">透明度</param>
    /// <param name="position">位置</param>
    /// <param name="PicturePath">文件路径</param>
    /// <returns></returns>
    public string DrawWords(string sourcePicture,
                                      string waterWords,
                                      float alpha,
                                      ImagePosition position,
                                      string PicturePath)
    {
        //
        // 判断参数是否有效
        //
        if (sourcePicture == string.Empty || waterWords == string.Empty || alpha == 0.0 || PicturePath == string.Empty)
        {
            return sourcePicture;
        }

        //
        // 源图片全路径
        //
        string sourcePictureName = PicturePath + sourcePicture;
        string fileExtension = System.IO.Path.GetExtension(sourcePictureName).ToLower();

        //
        // 判断文件是否存在,以及文件名是否正确
        //
        if (System.IO.File.Exists(sourcePictureName) == false || (
            fileExtension != ".gif"  &&
            fileExtension != ".jpg" &&
            fileExtension != ".png" ))
        {
            return sourcePicture;
        }

        //
        // 目标图片名称及全路径
        //
        string targetImage = sourcePictureName.Replace(System.IO.Path.GetExtension(sourcePictureName), "") + "_0703.jpg";

        //创建一个图片对象用来装载要被添加水印的图片
        Image imgPhoto = Image.FromFile(sourcePictureName);

        //