public class ValidationCodeHelper

    {

        //用户存取验证码字符串

        public string validationCode = String.Empty;

        Random ram = new Random();

        Graphics g = null;

        int bgWidth = ;

        int bgHeight = ;

        public string FontFace = "Consolas";

        public int FontSize = ;

        public Color foreColor = Color.FromArgb(, , );

        public Color backColor = Color.FromArgb(, , );

        public Color mixedLineColor = Color.FromArgb(, , );

        public int mixedLineWidth = ;

        public int mixedLineCount = ;

        #region 根据指定长度，返回随机验证码

        /// <summary>

        /// 根据指定长度，返回随机验证码

        /// </summary>

        /// <param name="length">制定长度</param>

        /// <returns>随即验证码</returns>

        public string Next(int length)

        {

            this.validationCode = GetRandomCode(length);

            return this.validationCode;

        }

        #endregion

        #region 根据指定长度及背景图片样式，返回带有随机验证码的图片对象

        /// <summary>

        /// 根据指定长度及背景图片样式，返回带有随机验证码的图片对象

        /// </summary>

        /// <param name="length">指定长度</param>

        /// <param name="hatchStyle">背景图片样式</param>

        /// <returns>Image对象</returns>

        public Image NextImage(int length, bool allowMixedLines,out string code)

        {

            this.validationCode = GetRandomCode(length);

            code = this.validationCode;

            //System.Web.HttpContext.Current.Session["Code"] = validationCode;

            //校验码字体

            Font myFont = new Font(FontFace, FontSize);

            //根据校验码字体大小算出背景大小

            bgWidth = (int)myFont.Size * length + ;

            bgHeight = (int)myFont.Size * ;

            //生成背景图片

            Bitmap myBitmap = new Bitmap(bgWidth, bgHeight);

            g = Graphics.FromImage(myBitmap);

            this.DrawBackground();

            this.DrawValidationCode(this.validationCode, myFont);

            if (allowMixedLines)

                this.DrawMixedLine();

            return (Image)myBitmap;

        }

        #endregion

        #region 内部方法：绘制验证码背景

        private void DrawBackground( )

        {

            //设置填充背景时用的笔刷

            HatchBrush hBrush = new HatchBrush(HatchStyle.Wave, backColor);

            //填充背景图片

            g.FillRectangle(hBrush, , , this.bgWidth, this.bgHeight);

        }

        #endregion

        #region 内部方法：绘制验证码

        private void DrawValidationCode(string vCode, Font font)

        {

            g.DrawString(vCode, font, new SolidBrush(this.foreColor), , );

        }

        #endregion

        #region 内部方法：绘制干扰线条

        /// <summary>

        /// 绘制干扰线条

        /// </summary>

        private void DrawMixedLine()

        {

            for (int i = ; i < mixedLineCount; i++)

            {

                g.DrawBezier(

                    new Pen(new SolidBrush(mixedLineColor),mixedLineWidth),

                    RandomPoint(),

                    RandomPoint(),

                    RandomPoint(),

                    RandomPoint()

                );

            }

        }

        #endregion

        #region 内部方法：返回指定长度的随机验证码字符串

        /// <summary>

        /// 根据指定大小返回随机验证码

        /// </summary>

        /// <param name="length">字符串长度</param>

        /// <returns>随机字符串</returns>

        private string GetRandomCode(int length)

        {

            StringBuilder sb = new StringBuilder();

            for (int i = ; i < length; i++)

            {

                sb.Append(Char.ConvertFromUtf32(RandomAZ09()));

            }

            return sb.ToString();

        }

        #endregion

        #region 内部方法：产生随机数和随机点

        /// <summary>

        /// 产生0-9A-Z的随机字符代码

        /// </summary>

        /// <returns>字符代码</returns>

        private int RandomAZ09()

        {

            //Thread.Sleep(15);

            int result = ;

            int i = ram.Next();

            switch (i)

            {

                case :

                    result = ram.Next(, );

                    break;

                case :

                    result = ram.Next(, );

                    break;

            }

            return result;

        }

        /// <summary>

        /// 返回一个随机点，该随机点范围在验证码背景大小范围内

        /// </summary>

        /// <returns>Point对象</returns>

        private Point RandomPoint()

        {

            //Thread.Sleep(15);

            Point point = new Point(ram.Next(this.bgWidth), ram.Next(this.bgHeight));

            return point;

        }

        #endregion

    } 

        public ActionResult Get()

        {

            ValidationCodeHelper vCode = new ValidationCodeHelper();

            string code;

            Image imgcode = vCode.NextImage(,true,out code);

            //设置临时数据字典进行储存

            this.TempData["Code"] = code;  

            //创建存储区为内存的流(关闭程序后,数据会被自动回收)

            MemoryStream ms = new MemoryStream();

            //将此图像以指定的格式保存到指定的流中

            imgcode.Save(ms,ImageFormat.Gif);

            this.Response.ContentType = "image/gif";

            this.Response.BinaryWrite(ms.ToArray());

            ms.Close();

            imgcode.Dispose();

            return new EmptyResult();

        } 

<script type="text/javascript">

    function imgCodes() {

        $("#valiCode").attr("src", '@Url.Action("Get", "ValidateCodeImg")'+"?time="+(new Date()).getTime());

    }

</script>

<td height="" class="login-text02">

    验证码：<br />

</td>

<td>

    <div style="width:400px;">

    <input type="text" name="txtCheck" />&nbsp;&nbsp;&nbsp;

    <img id="valiCode" style="cursor: pointer;" src="/ValidateCodeImg/Get" title="看不清，点击换一张" alt="看不清？请点我" onclick="imgCodes(this);" />

    &nbsp;&nbsp;

    <a href="javascript:imgCodes();">看不清楚,点击这里</a>

    </div>

</td>