验证码

我是用JSP的,,至于ASP不清楚.


在用户看到验证码的页面里有句:
<script>document.write("<img border=0 src=image.jsp?rand="+Math.random()*10000+">" ;</script>

<%@ page contentType="image/jpeg" import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*" %>
<%
// 在内存中创建图象
int width=60, height=20;
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);

// 获取图形上下文
Graphics g = image.getGraphics();

// 设定背景色
g.setColor(Color.white);
g.fillRect(0, 0, width, height);

//画边框
g.setColor(Color.black);
g.drawRect(0,0,width-1,height-1);

// 取随机产生的认证码(4位数字)
String rand = request.getParameter("rand");
rand = rand.substring(0,rand.indexOf("."));
switch(rand.length())
{
	case 1: rand = "000"+rand; break;
	case 2: rand = "00"+rand; break;
	case 3: rand = "0"+rand; break;
	default: rand = rand.substring(0,4); break;
}

// 将认证码存入SESSION
session.setAttribute("rand",rand);

// 将认证码显示到图象中
g.setColor(Color.black);
g.setFont(new Font("Times New Roman",Font.PLAIN,18));
g.drawString(rand,10,15);

// 随机产生88个干扰点，使图象中的认证码不易被其它程序探测到
Random random = new Random();
for (int i=0;i<88;i++)
{
	int x = random.nextInt(width);
	int y = random.nextInt(height);
	g.drawLine(x,y,x,y);
}

// 图象生效
g.dispose();

// 输出图象到页面
ImageIO.write(image, "JPEG", response.getOutputStream());

%> 

上面是产生图片的JSP文件,我觉得思想也一样,参考参考