asp.net简单数字验证码的实现

调用
验证码：<input type="text" id="txtValidate" style="border: solid 1px #9B9B9B; width: 85px;
height: 17px;" />  <img src="Rnd.aspx" mce_src="Rnd.aspx" style="width: 58px; height: 17px;
border: solid 1px #9B9B9B" align="absmiddle" />
后台实现
Rnd.aspx.cs
using System;
using System.Collections;
using System.Configuration;
using System.Data;
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.Drawing;
using System.Drawing.Imaging;
public partial class Rnd : System.Web.UI.Page
{
private int codeLen = 5;//随机显示字符个数
private int fineness = 100;//图片清晰度
private int imgWidth = 65;//图片宽度
private int imgHeight = 20;//图片高度
private string fontFamily = "Roman";//字体名称
private int fontSize = 12; //字体大小
private Random random = new Random();
protected void Page_Load(object sender, EventArgs e)
{
string validateCode = CreateValidateCode();
Session["RandomNumber"] = validateCode;
Bitmap bitmap = new Bitmap(imgWidth, imgHeight);
DisturbBitmap(bitmap);
DrawValidateCode(bitmap, validateCode);
bitmap.Save(Response.OutputStream, ImageFormat.Gif);
}
private string CreateValidateCode()//得到随机数
{
string validateCode = "";
for (int i = 0; i < codeLen; i++)
{
int n = random.Next(10);//返回一个小于最大值得随机数
validateCode += n.ToString();
}
return validateCode;
}
private void DisturbBitmap(Bitmap bitmap)//获取背景图
{
for (int i = 0; i < bitmap.Width; i++)
{
for (int j = 0; j < bitmap.Height; j++)
{
if (random.Next(90) <= this.fineness)
{