mvc中实现图片验证码很简单，只需要创建一个 FileContentResult的方法，返回file就行

/// <summary>
 /// 创建一个文件方法
 /// </summary>
 /// <returns></returns>
 public FileContentResult GetCode() {
 //参数一：产生几个字符的验证码图片 参数二：验证码的形式(数字、字母、数字字母混合都有)
 ValidateCode validCode = new ValidateCode(5, ValidateCode.CodeType.Alphas);
 //将图片转换为二进制
 MemoryStream ms =validCode.CreateCheckCodeImage() as MemoryStream;
 dateCode = validCode.CheckCode; //通过 CheckCode获取当前的验证码
 byte[] buffurPic = ms.ToArray(); 
 return File(buffurPic, "image/jpeg"); 
 
 }

以下是生成验证码代码：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
 
using System.Drawing;
using System.Drawing.Drawing2D;
using System.IO;
 
namespace Helper
{
 public class ValidateCode
 {
 
 
 #region Private Fields 
 private const double PI = 3.141592653579323846233832795; 
 private const double PI2 = 6.2831853071795876925286766559; 
 //private readonly int _wordsLen = 4; 
 private int _len;
 private CodeType _codetype;
 private readonly Single _jianju = (float)18.0; 
 private readonly Single _height = (float)24.0; 
 private string _checkCode; 
 #endregion 
 #region Public Property 
 public string CheckCode
 {
 
 get
 {
 
 return _checkCode;
 
 }
 
 }
 
 #endregion
 
 #region Constructors 
 /// 
 /// public constructors 
 /// 
 /// 验证码长度 
 /// 验证码类型：字母、数字、字母+ 数字 
 
 public ValidateCode(int len, CodeType ctype)
 { 
 this._len = len; 
 this._codetype = ctype;
 
 }
 
 #endregion 
 #region Public Field 
 public enum CodeType { Words, Numbers, Characters, Alphas } 
 #endregion 
 #region Private Methods
 
 public string GenerateNumbers()
 {
 
 string strOut = ""; 
 System.Random random = new Random();
 for (int i = 0; i < _len; i++)
 {
 string num = Convert.ToString(random.Next(10000) % 10); 
 strOut += num;
 
 }
 
 return strOut.Trim();
 
 }
 
 
 
 public string GenerateCharacters()
 {
 
 string strOut = ""; 
 System.Random random = new Random(); 
 for (int i = 0; i < _len; i++)
 {
 string num = Convert.ToString((char)(65 + random.Next(10000) % 26)); 
 strOut += num;
 
 }
 
 return strOut.Trim(); 
 }
 
 // 
 
 public string GenerateAlphas()
 {
 string strOut = ""; 
 string num = ""; 
 System.Random random = new Random();
 for (int i = 0; i < _len; i++)
 {
 
 if (random.Next(500) % 2 == 0)
 {
 num = Convert.ToString(random.Next(10000) % 10);
 
 }
 
 else
 { 
 num = Convert.ToString((char)(65 + random.Next(10000) % 26));
 
 }
 
 strOut += num;
 
 }
 return strOut.Trim();
 
 }
 
 
 
 private System.Drawing.Bitmap TwistImage(Bitmap srcBmp, bool bXDir, double dMultValue, double dPhase)
 {
 System.Drawing.Bitmap destBmp = new Bitmap(srcBmp.Width, srcBmp.Height);
 
 // 将位图背景填充为白色 
 System.Drawing.Graphics graph = System.Drawing.Graphics.FromImage(destBmp); 
 graph.FillRectangle(new SolidBrush(System.Drawing.Color.White), 0, 0, destBmp.Width, destBmp.Height); 
 graph.Dispose(); 
 
 double dBaseAxisLen = bXDir ? (double)destBmp.Height : (double)destBmp.Width;
 
 for (int i = 0; i < destBmp.Width; i++)
 { 
 for (int j = 0; j < destBmp.Height; j++)
 { 
 double dx = 0;
 dx = bXDir ? (PI2 * (double)j) / dBaseAxisLen : (PI2 * (double)i) / dBaseAxisLen;
 dx += dPhase; 
 double dy = Math.Sin(dx);
 

 // 取得当前点的颜色 
 int nOldX = 0, nOldY = 0;
 nOldX = bXDir ? i + (int)(dy * dMultValue) : i;
 nOldY = bXDir ? j : j + (int)(dy * dMultValue);
 
 System.Drawing.Color color = srcBmp.GetPixel(i, j);
 if (nOldX >= 0 && nOldX < destBmp.Width 
 && nOldY >= 0 && nOldY < destBmp.Height)
 {
 
 destBmp.SetPixel(nOldX, nOldY, color);
 
 }
 
 }
 
 }
 
 
 
 return destBmp;
 
 }
 
 #endregion 
 #region Public Methods
 
 public Stream CreateCheckCodeImage()
 {
 
 string checkCode; 
 switch (_codetype)
 {
 
 case CodeType.Alphas:
 checkCode = GenerateAlphas();
 break;
 
 case CodeType.Numbers:
 checkCode = GenerateNumbers();
 break;
 
 case CodeType.Characters: 
 checkCode = GenerateCharacters(); 
 break; 
 default:
 
 checkCode = GenerateAlphas();
 
 break;
 
 }
 
 this._checkCode = checkCode; 
 MemoryStream ms = null;
 
 // 
 
 if (checkCode == null || checkCode.Trim() == String.Empty)
 
 return null;
 
 Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * _jianju)), (int)_height);
 Graphics g = Graphics.FromImage(image);
 
 try
 {
 
 Random random = new Random(); 
 g.Clear(Color.White); 
 // 画图片的背景噪音线 
 for (int i = 0; i < 18; i++)
 {
 int x1 = random.Next(image.Width); 
 int x2 = random.Next(image.Width);
 int y1 = random.Next(image.Height);
 int y2 = random.Next(image.Height);
 
 g.DrawLine(new Pen(Color.FromArgb(random.Next()), 1), x1, y1, x2, y2);
 
 }
 
 Font font = new System.Drawing.Font("Times New Roman", 14, System.Drawing.FontStyle.Bold); 
 LinearGradientBrush brush = new LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
 
 if (_codetype != CodeType.Words)
 {
 
 for (int i = 0; i < checkCode.Length; i++)
 {
 
 g.DrawString(checkCode.Substring(i, 1), font, brush, 2 + i * _jianju, 1);
 
 }
 
 }
 else
 {
 
 g.DrawString(checkCode, font, brush, 2, 2);
 
 }
 
 // 画图片的前景噪音点 
 
 for (int i = 0; i < 150; i++)
 {
 
 int x = random.Next(image.Width); 
 int y = random.Next(image.Height); 
 image.SetPixel(x, y, Color.FromArgb(random.Next()));
 
 }
 
 // 画图片的波形滤镜效果 
 
 if (_codetype != CodeType.Words)
 {
 
 image = TwistImage(image, true, 3, 1);
 
 }
 
 // 画图片的边框线 
 
 g.DrawRectangle(new Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1); 
 ms = new System.IO.MemoryStream(); 
 image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
 
 }
 
 finally
 {
 
 g.Dispose(); 
 image.Dispose();
 
 }
 
 return ms;
 
 }
 
 #endregion
 
 
 }
}