突然想試試圖片水印的功能，就在網上收集了一些，記錄下來，便於以後學習。

創建一個類，調用其方法即可，可根據自己需求修改代碼。

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

namespace WaterMarkCommon
{
    public class WaterMark
    {
        /// <summary>
        /// 圖片水印
        
 
/// </summary>
        /// <param name="imgPath">服務器圖片相對路徑</param>
        /// <param name="filename">保存文件名</param>
        /// <param name="watermarkFilename">水印文件相對路徑</param>
        /// <param name="watermarkStatus">圖片水印位置 0=不使用 1=左上 2=中上 3=右上 4=左中  9=右下</param>
        ///
 
 <param name="quality">附加水印圖片質量,0-100</param>
        /// <param name="watermarkTransparency">水印的透明度 1--10 10為不透明</param>
        public static void AddImageSignPic(string imgPath, string filename, string watermarkFilename, int watermarkStatus, int quality, int watermarkTransparency)
        {
            
 
if(!File.Exists(GetMapPath(imgPath)))
                return;
            byte[] _ImageBytes = File.ReadAllBytes(GetMapPath(imgPath));
            Image img = Image.FromStream(new System.IO.MemoryStream(_ImageBytes));
            filename = GetMapPath(filename);

            if (watermarkFilename.StartsWith("/") == false)
                watermarkFilename = "/" + watermarkFilename;
            watermarkFilename =GetMapPath(watermarkFilename);
            if (!File.Exists(watermarkFilename))
                return;
            Graphics g = Graphics.FromImage(img);
            //設置高質量插值法
            //g.InterpolationMode = System.Drawing.Drawing2D.InterpolationMode.High;
            //設置高質量,低速度呈現平滑程度
            //g.SmoothingMode = System.Drawing.Drawing2D.SmoothingMode.HighQuality;
            Image watermark = new Bitmap(watermarkFilename);

            if (watermark.Height >= img.Height || watermark.Width >= img.Width)
                return;

            ImageAttributes imageAttributes = new ImageAttributes();
            ColorMap colorMap = new ColorMap();

            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 transparency = 0.5F;
            if (watermarkTransparency >= 1 && watermarkTransparency <= 10)
                transparency = (watermarkTransparency / 10.0F);


            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,  transparency, 0.0f},
                                                new float[] {0.0f,  0.0f,  0.0f,  0.0f, 1.0f}
                                            };

            ColorMatrix colorMatrix = new ColorMatrix(colorMatrixElements);

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

            int xpos = 0;
            int ypos = 0;

            switch (watermarkStatus)
            {
                case 1:
                    xpos = (int)(img.Width * (float).01);
                    ypos = (int)(img.Height * (float).01);
                    break;
                case 2:
                    xpos = (int)((img.Width * (float).50) - (watermark.Width / 2));
                    ypos = (int)(img.Height * (float).01);
                    break;
                case 3:
                    xpos = (int)((img.Width * (float).99) - (watermark.Width));
                    ypos = (int)(img.Height * (float).01);
                    break;
                case 4:
                    xpos = (int)(img.Width * (float).01);
                    ypos = (int)((img.Height * (float).50) - (watermark.Height / 2));
                    break;
                case 5:
                    xpos = (int)((img.Width * (float).50) - (watermark.Width / 2));
                    ypos = (int)((img.Height * (float).50) - (watermark.Height / 2));
                    break;
                case 6:
                    xpos = (int)((img.Width * (float).99) - (watermark.Width));
                    ypos = (int)((img.Height * (float).50) - (watermark.Height / 2));
                    break;
                case 7:
                    xpos = (int)(img.Width * (float).01);
                    ypos = (int)((img.Height * (float).99) - watermark.Height);
                    break;
                case 8:
                    xpos = (int)((img.Width * (float).50) - (watermark.Width / 2));
                    ypos = (int)((img.Height * (float).99) - watermark.Height);
                    break;
                case 9:
                    xpos = (int)((img.Width * (float).99) - (watermark.Width));
                    ypos = (int)((img.Height * (float).99) - watermark.Height);
                    break;
            }

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

            ImageCodecInfo[] codecs = ImageCodecInfo.GetImageEncoders();
            ImageCodecInfo ici = null;
            foreach (ImageCodecInfo codec in codecs)
            {
                if (codec.MimeType.IndexOf("jpeg") > -1)
                    ici = codec;
            }
            EncoderParameters encoderParams = new EncoderParameters();
            long[] qualityParam = new long[1];
            if (quality < 0 || quality > 100)
                quality = 80;

            qualityParam[0] = quality;

            EncoderParameter encoderParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, qualityParam);
            encoderParams.Param[0] = encoderParam;

            if (ici != null)
                img.Save(filename, ici, encoderParams);
            else
                img.Save(filename);

            g.Dispose();
            img.Dispose();
            watermark.Dispose();
            imageAttributes.Dispose();
        }

        /// <summary>
        /// 文字水印
        /// </summary>
        /// <param name="imgPath">服務器圖片相對路徑</param>
        /// <param name="filename">保存文件名</param>
        /// <param name="watermarkText">水印文字</param>
        /// <param name="watermarkStatus">圖片水印位置 0=不使用 1=左上 2=中上 3=右上 4=左中  9=右下</param>
        /// <param name="quality">附加水印圖片質量,0-100</param>
        /// <param name="fontsize">字體大小</param>
        /// <param name="fontname">字體</param>
        public static void AddImageSignText(string imgPath, string filename, string watermarkText, int watermarkStatus, int quality, int fontsize ,string fontname = "微軟雅黑")
        {
            byte[] _ImageBytes = File.ReadAllBytes(GetMapPath(imgPath));
            Image img = Image.FromStream(new System.IO.MemoryStream(_ImageBytes));
            filename = GetMapPath(filename);

            Graphics g = Graphics.FromImage(img);
            Font drawFont = new Font(fontname, fontsize, FontStyle.Regular, GraphicsUnit.Pixel);
            SizeF crSize;
            crSize = g.MeasureString(watermarkText, drawFont);

            float xpos = 0;
            float ypos = 0;

            switch (watermarkStatus)
            {
                case 1:
                    xpos = (float)img.Width * (float).01;
                    ypos = (float)img.Height * (float).01;
                    break;
                case 2:
                    xpos = ((float)img.Width * (float).50) - (crSize.Width / 2);
                    ypos = (float)img.Height * (float).01;
                    break;
                case 3:
                    xpos = ((float)img.Width * (float).99) - crSize.Width;
                    ypos = (float)img.Height * (float).01;
                    break;
                case 4:
                    xpos = (float)img.Width * (float).01;
                    ypos = ((float)img.Height * (float).50) - (crSize.Height / 2);
                    break;
                case 5:
                    xpos = ((float)img.Width * (float).50) - (crSize.Width / 2);
                    ypos = ((float)img.Height * (float).50) - (crSize.Height / 2);
                    break;
                case 6:
                    xpos = ((float)img.Width * (float).99) - crSize.Width;
                    ypos = ((float)img.Height * (float).50) - (crSize.Height / 2);
                    break;
                case 7:
                    xpos = (float)img.Width * (float).01;
                    ypos = ((float)img.Height * (float).99) - crSize.Height;
                    break;
                case 8:
                    xpos = ((float)img.Width * (float).50) - (crSize.Width / 2);
                    ypos = ((float)img.Height * (float).99) - crSize.Height;
                    break;
                case 9:
                    xpos = ((float)img.Width * (float).99) - crSize.Width;
                    ypos = ((float)img.Height * (float).99) - crSize.Height;
                    break;
            }

            g.DrawString(watermarkText, drawFont, new SolidBrush(Color.White), xpos + 1, ypos + 1);
            g.DrawString(watermarkText, drawFont, new SolidBrush(Color.Black), xpos, ypos);

            ImageCodecInfo[] codecs = ImageCodecInfo.GetImageEncoders();
            ImageCodecInfo ici = null;
            foreach (ImageCodecInfo codec in codecs)
            {
                if (codec.MimeType.IndexOf("jpeg") > -1)
                    ici = codec;
            }
            EncoderParameters encoderParams = new EncoderParameters();
            long[] qualityParam = new long[1];
            if (quality < 0 || quality > 100)
                quality = 80;

            qualityParam[0] = quality;

            EncoderParameter encoderParam = new EncoderParameter(System.Drawing.Imaging.Encoder.Quality, qualityParam);
            encoderParams.Param[0] = encoderParam;

            if (ici != null)
                img.Save(filename, ici, encoderParams);
            else
                img.Save(filename);

            g.Dispose();
            img.Dispose();
        }

        #region 獲得當前絕對路徑
        /// <summary>
        /// 獲得當前絕對路徑
        /// </summary>
        /// <param name="strPath">指定的路徑</param>
        /// <returns>絕對路徑</returns>
        public static string GetMapPath(string strPath)
        {
            if (strPath.ToLower().StartsWith("http://"))
            {
                return strPath;
            }
            if (HttpContext.Current != null)
            {
                return HttpContext.Current.Server.MapPath(strPath);
            }
            else //非web程序引用
            {
                strPath = strPath.Replace("/", "\\");
                if (strPath.StartsWith("\\"))
                {
                    strPath = strPath.Substring(strPath.IndexOf(‘\\‘, 1)).TrimStart(‘\\‘);
                }
                return System.IO.Path.Combine(AppDomain.CurrentDomain.BaseDirectory, strPath);
            }
        }
        #endregion
    }
}

C# 圖片添加水印