验证码技术是网站开发过程中比较重要的技术，可以防止非法人员利用注册机或者登陆工具来攻击我们的网站。下面是效果图：
具体实现方法如下：
1、主要思路是：引用Using System.Drawing命名空间，利用Graphics的FromImage方法创建一个画布，同时设置画布的宽和高，然后通过Graphics类 的DrawString方法随机生成的字符串绘制到画布中，绘制验证码的同时，在画布中利用SetPixel方法绘制一些色点，从而防止非法人员利用机器 人来进行登陆。当我们绘制验证码完毕后，在需要验证码的页面中利用Image空间将其显示出来，Image控件显示验证码的HTML源码设置如下：
<asp:Image ID="Image1" runat="server"ImageUrl="~/ValidateNum.aspx" />
<asp:LinkButton ID="LinkButton1" runat="server" style="font-size: small; ">看不清，换一张</asp:LinkButton>
2、这里所用到的ValidateNum.aspx页面代码如下：
using System;
using System.Collections;
using System.Configuration;
using System.Data;
using System.Linq;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.HtmlControls;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Xml.Linq;
using System.Drawing; public partial class ValidateNum : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
string validateNum = CreateRandomNum();//成生4位随机字符串
CreateImage(validateNum);//将生成的随机字符串绘成图片
Session["ValidateNum"] = validateNum;//保存验证码
}
}
//生成随机字符串
private string CreateRandomNum(int NumCount)
{
string allChar = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,W,X,Y,Z";
string[] allCharArray = allChar.Split(',');//拆分成数组
string randomNum = "";
int temp = -;//记录上次随机数的数值，尽量避免产生几个相同的随机数 Random rand = new Random();
for (int i = ; i < NumCount; i++)
{
if (temp != -)
{
rand = new Random(i * temp * ((int)DateTime.Now.Ticks));
}
int t = rand.Next();
if (temp == t)
{
return CreateRandomNum(NumCount);
}
temp = t;
randomNum += allCharArray[t];
}
return randomNum;
}
//生成图片
private void CreateImage(string validateNum)
{
if (validateNum == null || validateNum.Trim() == String.Empty)
return;
//生成Bitmap图像
System.Drawing.Bitmap image = new System.Drawing.Bitmap(validateNum.Length * + , );
Graphics g = Graphics.FromImage(image); try
{
//生成随机生成器
Random random = new Random(); //清空图片背景色
g.Clear(Color.White); //画图片的背景噪音线
for (int i = ; i < ; 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.Silver), x1, y1, x2, y2);
} Font font = new System.Drawing.Font("Arial", , (System.Drawing.FontStyle.Bold | System.Drawing.FontStyle.Italic));
System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(, , image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2f, true);
g.DrawString(validateNum, font, brush, , ); //画图片的前景噪音点
for (int i = ; i < ; i++)
{
int x = random.Next(image.Width);
int y = random.Next(image.Height); image.SetPixel(x, y, Color.FromArgb(random.Next()));
} //画图片的边框线
g.DrawRectangle(new Pen(Color.Silver), , , image.Width - , image.Height - ); System.IO.MemoryStream ms = new System.IO.MemoryStream();
//将图像保存到指定的流
image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
Response.ClearContent();
Response.ContentType = "image/Gif";
Response.BinaryWrite(ms.ToArray());
}
finally
{
g.Dispose();
image.Dispose();
}
}
}