深圳网站制作公司中如何去实现asp.net(c#)验证码

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.IO;
namespace jgy_keshi_lyb
{
public partial class checkimage : System.Web.UI.Page
{
Random ran = new Random();
protected void Page_Load(object sender, Eventargs e)
{
string str = getRandomValidate(4);
Session["check"] = str;
//这一步是为了将验证码写入Session，进行验证，不能缺省，也可一使用cookie
getImageValidate(str);
}
//得到随机字符串,长度自己定义
private string getRandomValidate(int len)
{
int num;
int tem;
string rtuStr = "";
for (int i = 0; i < len; i++)
{
num = ran.Next();
/*
* 这里可以选择生成字符和数字组合的验证码
*/
tem = num % 10 + 0;//生成数字
//tem = num % 26 + a;//生成字符
rtuStr += Convert.ToChar(tem).ToString();
}
return rtuStr;
}
//生成图像
private void getImageValidate(string strValue)
{
//string str = "OO00"; //前两个为字母O，后两个为数字0
int width = Convert.ToInt32(strValue.Length * 12); //计算图像宽度
Bitmap img = new Bitmap(width, 23);
Graphics gfc = Graphics.FromImage(img); //产生Graphics对象，进行画图
gfc.Clear(Color.White);
drawLine(gfc, img);
//写验证码，需要定义font
font font = new font("arial", 12, fontStyle.Bold);
System.Drawing.Drawing2D.LinearGradientBrush brush =
new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, img.Width, img.Height), Color.DarkOrchid, Color.Blue, 1.5f, true);
gfc.DrawString(strValue, font, brush, 3, 2);
drawPoint(img);
gfc.DrawRectangle(new Pen(Color.DarkBlue), 0, 0, img.Width - 1, img.Height - 1);
//将图像添加到页面
MemoryStream ms = new MemoryStream();
img.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
//更改Http头
Response.ClearContent();
Response.ContentType = "image/gif";
Response.BinaryWrite(ms.Toarray());
//Dispose
gfc.Dispose();
img.Dispose();
Response.End();
}
private void drawLine(Graphics gfc, Bitmap img)
{
//选择画10条线,也可以增加，也可以不要线，只要随机杂点即可
for (int i = 0; i < 10; i++)
{
int x1 = ran.Next(img.Width);
int y1 = ran.Next(img.Height);
int x2 = ran.Next(img.Width);
int y2 = ran.Next(img.Height);
gfc.DrawLine(new Pen(Color.Silver), x1, y1, x2, y2); //注意画笔一定要浅颜色，否则验证码看不清楚
}
}
private void drawPoint(Bitmap img)
{
/*
//选择画100个点,可以根据实际情况改变
for (int i = 0; i < 100; i++)
{
int x = ran.Next(img.Width);
int y = ran.Next(img.Height);
img.SetPixel(x,y,Color.Fromargb(ran.Next()));//杂点颜色随机
}
*/
int col = ran.Next();//在一次的图片中杂店颜色相同
for (int i = 0; i < 100; i++)
{
int x = ran.Next(img.Width);
int y = ran.Next(img.Height);
img.SetPixel(x, y, Color.Fromargb(col));
}
}

}
}

<img src="checkimage.aspx"
alt=看不清楚，双击图片换一张。
ondblclick="this.src= checkimage.aspxflag= + Math.random() "
border="1" height="24" />