Mvc验证码

前端代码
<img alt="验证码图片" class="img" onclick="refresh(this)" src="/Fifth/VerifyCode" title="点击刷新">
<script>
    function refresh(obj) {
        $(obj).attr("src", "/Fifth/Verify?random=" + Math.random());
    }
</script>

后台Action（2种方式）
        /// <summary>
        /// 验证码 直接返回File：方式一
        /// </summary>
        /// <returns></returns>
        public ActionResult VerifyCode()
        {
            string code = "";
            Bitmap bitmap = VerifyCodeHelper.CreateVerifyCode(out code);
            base.HttpContext.Session["CheckCode"] = code;//Session识别用户，为单一用户有效
            MemoryStream stream = new MemoryStream();
            bitmap.Save(stream, ImageFormat.Gif);
            return File(stream.ToArray(), "image/gif");//返回FileContentResult图片
        }

        /// <summary>
        /// 验证码  直接写入Response：方式二
        /// </summary>
        public void Verify()
        {
            string code = "";
            Bitmap bitmap = VerifyCodeHelper.CreateVerifyCode(out code);
            base.HttpContext.Session["CheckCode"] = code;
            bitmap.Save(base.Response.OutputStream, ImageFormat.Gif);
            base.Response.ContentType = "image/gif";
        }

生成验证码图片代码
    public class VerifyCodeHelper
    {
        public static Bitmap CreateVerifyCode(out string code)
        {
            //建立Bitmap对象，绘图
            Bitmap bitmap = new Bitmap(200, 60);
            Graphics graph = Graphics.FromImage(bitmap);
            graph.FillRectangle(new SolidBrush(Color.White), 0, 0, 200, 60);
            Font font = new Font(FontFamily.GenericSerif, 48, FontStyle.Bold, GraphicsUnit.Pixel);
            Random r = new Random();
            string letters = "ABCDEFGHIJKLMNPQRSTUVWXYZ0123456789";

            StringBuilder sb = new StringBuilder();

            //添加随机的五个字母
            for (int x = 0; x < 5; x++)
            {
                string letter = letters.Substring(r.Next(0, letters.Length - 1), 1);
                sb.Append(letter);
                graph.DrawString(letter, font, new SolidBrush(Color.Black), x * 38, r.Next(0, 15));
            }
            code = sb.ToString();

            //混淆背景
            Pen linePen = new Pen(new SolidBrush(Color.Black), 2);
            for (int x = 0; x < 6; x++)
                graph.DrawLine(linePen, new Point(r.Next(0, 199), r.Next(0, 59)), new Point(r.Next(0, 199), r.Next(0, 59)));
            return bitmap;
        }
    }