图片水印

 public static void WarterImage(string bitmap, string watermark, string dest, string copyright, ImageFormat imageFormat)
        {
            //定义版权声明的字符串信息或文本
            string Copyright = copyright;

            //创建一个需要添加水印的图像对象
            Image imgPhoto = Image.FromFile(bitmap);

            int phWidth = imgPhoto.Width;
            int phHeight = imgPhoto.Height;

            //创建一个原始图像大小的Bitmap
            Bitmap bmPhoto = new Bitmap(phWidth, phHeight, PixelFormat.Format24bppRgb);

            bmPhoto.SetResolution(imgPhoto.HorizontalResolution, imgPhoto.VerticalResolution);

            //把Bitmap装载进Graphics对象 
            Graphics grPhoto = Graphics.FromImage(bmPhoto);

            //创建一个包含水印的image对象
            Image imgWatermark = new Bitmap(watermark);
            int wmWidth = imgWatermark.Width;
            int wmHeight = imgWatermark.Height;

            //------------------------------------------------------------
            //第一步 -插入版权信息
            //------------------------------------------------------------

            //设置这个要转换Graphics对象的图像质量
            grPhoto.SmoothingMode = SmoothingMode.AntiAlias;

            //绘制图像对象到graphics对象（保留原始的宽高）
            grPhoto.DrawImage(
                imgPhoto,                               // Photo Image object
                new Rectangle(0, 0, phWidth, phHeight), // 构造矩形
                0,                                      // 要绘制的源图像的x坐标 
                0,                                      // 要绘制的源图像的y坐标
                phWidth,                                // 要绘制的源图像的宽度
                phHeight,                               // 要绘制的源图像的高度
                GraphicsUnit.Pixel);                    // 图像所使用的单位

            //-------------------------------------------------------
            //为了最大化版权信息的字体，定一个了一个数组来包含不同的字体大小
            //-------------------------------------------------------
            int[] sizes = new int[] { 16, 14, 12, 10, 8, 6, 4 };

            Font crFont = null;
            SizeF crSize = new SizeF();

            //通过循环这个数组，来选用不同的字体大小
            //如果它的大小小于图像的宽度，就选用这个大小的字体
            for (int i = 0; i < 7; i++)
            {
                //设置字体，这里是用arial，黑体
                crFont = new Font("arial", sizes[i], FontStyle.Bold);
                //Measure the Copyright string in this Font
                crSize = grPhoto.MeasureString(Copyright, crFont);

                if ((ushort)crSize.Width < (ushort)phWidth)
                    break;
            }

            //因为图片的高度可能不尽相同, 所以定义了
            //从图片底部算起预留了5%的空间
            int yPixlesFromBottom = (int)(phHeight * .05);

            //现在使用版权信息字符串的高度来确定要绘制的图像的字符串的y坐标

            float yPosFromBottom = ((phHeight - yPixlesFromBottom) - (crSize.Height / 2));

            //计算x坐标
            float xCenterOfImg = (phWidth / 2);

            //把文本布局设置为居中
            StringFormat StrFormat = new StringFormat();
            StrFormat.Alignment = StringAlignment.Center;

            //通过Brush来设置黑色半透明
            SolidBrush semiTransBrush2 = new SolidBrush(Color.FromArgb(153, 0, 0, 0));

            //绘制版权字符串
            grPhoto.DrawString(Copyright,                 //版权字符串文本
                crFont,                                   //字体
                semiTransBrush2,                           //Brush
                new PointF(xCenterOfImg + 1, yPosFromBottom + 1),  //位置
                StrFormat);

            //设置成白色半透明
            SolidBrush semiTransBrush = new SolidBrush(Color.FromArgb(153, 255, 255, 255));

            //第二次绘制版权字符串来创建阴影效果
            //记住移动文本的位置1像素
            grPhoto.DrawString(Copyright,                 //版权文本
                crFont,                                   //字体
                semiTransBrush,                           //Brush
                new PointF(xCenterOfImg, yPosFromBottom),  //位置
                StrFormat);                               //文本对齐



            //------------------------------------------------------------
            //第二步：插入水印图像
            //------------------------------------------------------------

            //通过之前创建的Bitmap创建一个 Bitmap
            Bitmap bmWatermark = new Bitmap(bmPhoto);
            bmWatermark.SetResolution(imgPhoto.HorizontalResolution, imgPhoto.VerticalResolution);

            Graphics grWatermark = Graphics.FromImage(bmWatermark);

            ImageAttributes imageAttributes = new ImageAttributes();

            //第一步是用水印来替代背景颜色 
            //(Alpha=0, R=0, G=0, B=0)
            //要使用 Colormap 来定义一个RemapTable
            ColorMap colorMap = new ColorMap();

            //这个水印的背景定义成100%绿色，并用来替代透明           
            colorMap.OldColor = Color.FromArgb(255, 0, 255, 0);
            colorMap.NewColor = Color.FromArgb(0, 0, 0, 0);

            ColorMap[] remapTable = { colorMap };

            imageAttributes.SetRemapTable(remapTable, ColorAdjustType.Bitmap);

            //第二个颜色是用来控制水印图片的不透明度的 
            //是使用一个5*5的RGBA矩阵来实现的 
            // 设置第4行、第4列的值为0.3来不透明度的级别
            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}};
            ColorMatrix wmColorMatrix = new ColorMatrix(colorMatrixElements);

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

            //本例的水印放置在右上方
            // 偏移量是10

            int xPosOfWm = ((phWidth - wmWidth) - 10);
            int yPosOfWm = ((phHeight - wmHeight) - 10);

            grWatermark.DrawImage(imgWatermark,
                new Rectangle(xPosOfWm, yPosOfWm, wmWidth, wmHeight),  //Set the detination Position
                0,                  // x坐标
                0,                  // y坐标
                wmWidth,            // 水印宽度
                wmHeight,            // 水印高度
                GraphicsUnit.Pixel, // 单位
                imageAttributes);   //ImageAttributes对象

            //使用新生成的加了水印图片替代原始图片
            imgPhoto = bmWatermark;
            grPhoto.Dispose();
            grWatermark.Dispose();

            //保存的路径
            imgPhoto.Save(dest, imageFormat);
            imgPhoto.Dispose();
            imgWatermark.Dispose();
        }