static void Main(string[] args)
        {
            string savePath = @"E:/2013相片/上傳前/";
            string sourcePath = @"E:/2013相片/QQ空間使用/";
            string sourceName = "DSC_0216.JPG";
            int scale = 5;

            Image img = Image.FromFile(sourcePath + sourceName);
            int width = img.Width / scale;
            int height = img.Height / scale;

            Image imgNew = new Bitmap(width, height);
            Graphics g = Graphics.FromImage(imgNew);
            g.DrawImage(img, new System.Drawing.Rectangle(0, 0, width, height),
            new System.Drawing.Rectangle(0, 0, img.Width, img.Height),
            System.Drawing.GraphicsUnit.Pixel);

            imgNew.Save(savePath + "a.jpg", ImageFormat.Jpeg);
        }

class Program
    {
        static readonly string[] IMAGE_EXTNAME = new string[] { "jpg"};
        static void Main(string[] args)
        {
            string savePath = @"E:/2013相片/上傳前/";
            string sourcePath = @"E:/2013相片/QQ空間使用/";
            int scale = 5;

            List<string> imageNames = GetImageNames(sourcePath);
            if (imageNames != null && imageNames.Count > 0)
            {
                foreach (var item in imageNames)
                {
                    SaveSmallPhoto(sourcePath + item, scale, savePath + item);
                }
            }
        }

        /// <summary>
        /// 獲取路徑下所有符合指定圖片后綴文件名
        /// </summary>
        /// <param name="path">路徑</param>
        /// <returns></returns>
        static List<string> GetImageNames(string path)
        {
            string[] fileNames = Directory.GetFiles(path);
            if (fileNames == null || fileNames.Length == 0)
            {
                return null;
            }

            List<string> imageNames = new List<string>();
            foreach (var item in fileNames)
            {
                if (ExistsInExtName(item, IMAGE_EXTNAME))
                {
                    imageNames.Add(item.Substring(item.LastIndexOf('//') + 1));
                }
            }

            return imageNames;
        }

        /// <summary>
        /// 判斷文件名是否符合指定后綴名
        /// </summary>
        /// <param name="name">文件名</param>
        /// <param name="extNames">符合要求的后綴名</param>
        /// <returns></returns>
        static bool ExistsInExtName(string name, string[] extNames)
        {
            if (string.IsNullOrEmpty(name) || extNames == null || extNames.Length == 0)
            {
                return false;
            }

            foreach (var item in extNames)
            {
                if (name.ToLower().EndsWith(item))
                {
                    return true;
                }
            }

            return false;
        }

        /// <summary>
        /// 將圖片按比例縮小保存
        /// </summary>
        /// <param name="fromPath">原圖片路徑名</param>
        /// <param name="scale">縮小比例</param>
        /// <param name="toPath">縮小后保存的路徑名</param>
        static void SaveSmallPhoto(string fromPath, int scale, string toPath)
        {
            int width, height;
            using (Image img = Image.FromFile(fromPath))
            {
                width = img.Width / scale;
                height = img.Height / scale;

                using (Image imgNew = new Bitmap(width, height))
                {
                    using (Graphics g = Graphics.FromImage(imgNew))
                    {
                        g.DrawImage(img, new Rectangle(0, 0, width, height),
                            new Rectangle(0, 0, img.Width, img.Height), System.Drawing.GraphicsUnit.Pixel);
                    }

                    imgNew.Save(toPath, ImageFormat.Jpeg);
                }
            }
        }
    }