asp.net如何实现生成验证码的登录界面

先要新建validate aspx验证页面。然后生成验证码控件imagebutton，再生成picture窗体。
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;
using System.IO;
public partial class Picture : System.Web.UI.Page
{
Random ran = new Random();
protected void Page_Load(object sender, EventArgs e)
{
string str = getRandomValidate(4);
Session["CheckCode"] = str;//这一部是Wie了验证码写入Session,进行验证，也可以使用cookie
getImageValidate(str);
}
//得到随机字符串，长度自定义
private string getRandomValidate(int len)
{
int num;
int tem;
string rtuStr="";
for (int i = 0; i < len;i++ )
{
num = ran.Next();
tem = num % 10 + '0';//生成数字
//tem = num % 26 + 'A';//生成字符
rtuStr += Convert.ToChar(tem).ToString();public partial class Picture : System.Web.UI.Page
{
Random ran = new Random();
protected void Page_Load(object sender, EventArgs e)
{
string str = getRandomValidate(4);
Session["CheckCode"] = str;//这一部是Wie了验证码写入Session,进行验证，也可以使用cookie
getImageValidate(str);
}
//得到随机字符串，长度自定义
private string getRandomValidate(int len)
{
int num;
int tem;
string rtuStr="";
for (int i = 0; i < len;i++ )
{
num = ran.Next();
tem = num % 10 + '0';//生成数字
//tem = num % 26 + 'A';//生成字符
rtuStr += Convert.ToChar(tem).ToString();public partial class Picture : System.Web.UI.Page
{
Random ran = new Random();
protected void Page_Load(object sender, EventArgs e)
{
string str = getRandomValidate(4);
Session["CheckCode"] = str;//这一部是Wie了验证码写入Session,进行验证，也可以使用cookie
getImageValidate(str);
}
//得到随机字符串，长度自定义
private string getRandomValidate(int len)
{
int num;
int tem;
string rtuStr="";
for (int i = 0; i < len;i++ )
{
num = ran.Next();
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，后两个数为0
int width = Convert.ToInt32(strValue.Length*12);
Bitmap img = new Bitmap(width,23);
Graphics gfc = Graphics.FromImage(img);
gfc.Clear(Color.White);
drawLine(gfc,img);
//写验证码，要定义Font
Font font = new Font("arial",12,FontStyle.Bold);
//Font font = new Font("宋体",12,FontStyle.Bold|FontStyle.Italic);

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
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，只要随机杂点就行
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);//注意画笔要淡，不然看不清
}

}
//private void drawPoint(Bitmap img)
//{

//}
private void drawPoint(Bitmap img)
{
int col = ran.Next();//在一次的图片中杂点颜色相同
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));
}
}

}
这就是全部使用验证窗口源代码，