在项目中验证码的生成通常是需要页面无刷新的，所以验证码图片实际是跟在某个input后面的img，通过控制该img来控制验证码显示的位置，例如：

<div>

<input id="testcode" type="text"/><img id="testimg" src="../Home/codeindex"/>

<a href="javascript:freshimg()" style="font-size: 12px; color: Green;">看不清</a>

</div>

<div>

<img id="imgtest" width="500px" height="600px" src="~/pp.png" style="display:none"/>

</div>

需要做到无刷新的切换图片

function freshimg() {

var randomnum = Math.random();

var getimagecode = document.getElementById("testimg");

getimagecode.src = "../Home/codeindex? " + randomnum;

}

验证输入的验证码是否正确

$(document).ready(function () {

var PerformSearch;

$("#testcode").keyup(function () {

var va = $(this).val();

if (PerformSearch) clearTimeout(PerformSearch);

PerformSearch=setTimeout(function () {

$.ajax({

type: "post",

url: "../Home/CheckCode",

data: { valdatecode: va },

dataType: "text",

success: function (data) {

if (data == "true") {

alert("验证码输入正确");

document.getElementById("imgtest").style.display = "block";

}

else {

alert("验证码输入错误");

fresh();

document.getElementById("imgtest").style.display = "none";

}

}

});

}, 1000)

});

});

后台代码为

public ActionResult codeindex()  //该段代码转载其他文档

{

#region 方法1:调用类方法

//CreateValdateCode cc = new CreateValdateCode();

//cc.GetValDateCode();

//Session["code"] = cc.Code;

//return View();

#endregion

#region 方法二

string chkCode = string.Empty;

//颜色列表，用于验证码、噪线、噪点

Color[] color = { Color.Black, Color.Red, Color.Blue, Color.Green, Color.Orange, Color.Brown, Color.Brown, Color.DarkBlue };

//字体列表，用于验证码

string[] font = { "Times New Roman", "MS Mincho", "Book Antiqua", "Gungsuh", "PMingLiU", "Impact" };

//验证码的字符集，去掉了一些容易混淆的字符

char[] character = { '2', '3', '4', '5', '6', '8', '9', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'J', 'K', 'L', 'M', 'N', 'P', 'R', 'S', 'T', 'W', 'X', 'Y','a','b','c' };

Random rnd = new Random();

//生成验证码字符串

for (int i = 0; i < 4; i++)

{

chkCode += character[rnd.Next(character.Length)];

}

Session["code"] = chkCode;

Bitmap bmp = new Bitmap(100, 40);

Graphics g = Graphics.FromImage(bmp);

g.Clear(Color.White);

//画噪线

for (int i = 0; i < 10; i++)

{

int x1 = rnd.Next(100);

int y1 = rnd.Next(40);

int x2 = rnd.Next(100);

int y2 = rnd.Next(40);

Color clr = color[rnd.Next(color.Length)];

g.DrawLine(new Pen(clr), x1, y1, x2, y2);

}

//画验证码字符串

for (int i = 0; i < chkCode.Length; i++)

{

string fnt = font[rnd.Next(font.Length)];

Font ft = new Font(fnt, 18);

Color clr = color[rnd.Next(color.Length)];

g.DrawString(chkCode[i].ToString(), ft, new SolidBrush(clr), (float)i * 18 + 8, (float)8);

}

//画噪点

for (int i = 0; i < 100; i++)

{

int x = rnd.Next(bmp.Width);

int y = rnd.Next(bmp.Height);

Color clr = color[rnd.Next(color.Length)];

bmp.SetPixel(x, y, clr);

}

Response.Buffer = true;

Response.ExpiresAbsolute = System.DateTime.Now.AddMilliseconds(0);

Response.Expires = 0;

Response.CacheControl = "no-cache";

Response.AppendHeader("Pragma", "No-Cache");

MemoryStream ms = new MemoryStream();

try

{

bmp.Save(ms, ImageFormat.Png);

Response.ClearContent();

Response.ContentType = "image/Png";

Response.BinaryWrite(ms.ToArray());

}

finally

{

bmp.Dispose();

g.Dispose();

}

#endregion

return View();

}

public string CheckCode(string valdatecode)

{

if ( Session["code"].ToString().ToUpper()== valdatecode.ToUpper())

{

return "true";

}

else

{

return "false";

}

}