用C#实现生成验证码功能，具体步骤如下：
第一步，创建一个新的页面Code.aspx，在.cs文件中添加下面的代码：
using System.IO;using System.Drawing.Imaging;using System.Drawing.Drawing2D;using System.Drawing;public partial class Code : System.Web.UI.Page
...{
protected void Page_Load(object sender, EventArgs e)
...{ //先产生数字串 string Code = this.CreateRandomCode(4); //用session保存 Session["CheckCode"] = Code; //作图 CreateImage(Code);
} public string CreateRandomCode(int codeCount) //生成随机数 ...{ 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,V,W,X,Y,Z"; string[] allCharArray = allChar.Split(','); string randomCode = ""; int temp = -1; Random rand = new Random(); for (int i = 0; i < codeCount; i++) ...{ if (temp != -1) ...{ rand = new Random(i * temp * ((int)DateTime.Now.Ticks)); } int t = rand.Next(36); if (temp != -1 && temp == t) ...{ return CreateRandomCode(codeCount); } temp = t; randomCode += allCharArray[t]; } return randomCode; } private void CreateImage(string checkCode) ...{ int iwidth = (int)(checkCode.Length * 15); System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 25); Graphics g = Graphics.FromImage(image); g.Clear(Color.White); //定义颜色 Color[] c = ...{ Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple }; //定义字体 string[] font = ...{ "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial", "宋体" }; Random rand = new Random(); //随机输出噪点 for (int i = 0; i < 50; i++) ...{ int x = rand.Next(image.Width); int y = rand.Next(image.Height); g.DrawRectangle(new Pen(Color.LightGray, 0), x, y, 1, 1); } //输出不同字体和颜色的验证码字符 for (int i = 0; i < checkCode.Length; i++) ...{ int cindex = rand.Next(7); int findex = rand.Next(5); Font f = new System.Drawing.Font(font[findex], 12, System.Drawing.FontStyle.Bold); Brush b = new System.Drawing.SolidBrush(c[cindex]); int ii = 4; if ((i + 1) % 2 == 0) ...{ ii = 2; } g.DrawString(checkCode.Substring(i, 1), f, b, 3 + (i * 12), ii); } //画一个边框 g.DrawRectangle(new Pen(Color.Black, 0), 0, 0, image.Width - 1, image.Height - 1); //输出到浏览器 System.IO.MemoryStream ms = new System.IO.MemoryStream(); image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg); Response.ClearContent(); Response.ContentType = "image/Gif"; Response.BinaryWrite(ms.ToArray()); g.Dispose(); image.Dispose(); }
}第二步，在要使用验证码的页面加入一个<img />加载验证码页面：
<html xmlns="http://www.w3.org/1999/xhtml" ><head runat="server"> <title>无标题页</title></head><body> <form id="form1" runat="server"> <div> <asp:TextBox ID="TextBox1" runat="server"></asp:TextBox> <img alt="" src="Code.aspx" /> <asp:Button ID="Button1" runat="server" Text="Button" OnClick="Button1_Click" /> </div> </form></body></html>第三步，添加判断验证码输入是否正确的按钮事件Button1_Click：
protected void Button1_Click(object sender, EventArgs e) ...{ if (String.Compare(Session["CheckCode"].ToString(), TextBox1.Text, true) != 0) ...{ Response.Write("验证码错误，请输入正确的验证码。"); return; } else ...{ Response.Write("ok"); } }试试看吧！：）