这是jsp页面，起个名字例如叫image.jsp：

<%@ page contentType="image/JPEG"   
    import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*"   
    pageEncoding="GBK"%><%!Color getRandColor(int fc, int bc) {    
        Random random = new Random();    
        if (fc > 255)    
            fc = 255;    
        if (bc > 255)    
            bc = 255;    
        int r = fc + random.nextInt(bc - fc);    
        int g = fc + random.nextInt(bc - fc);    
        int b = fc + random.nextInt(bc - fc);    
        return new Color(r, g, b);    
    }%><%    
        
    response.setHeader("Pragma", "No-cache");    
    response.setHeader("Cache-Control", "no-cache");    
    response.setDateHeader("Expires", 0);    
       
    int width = 60, height = 20;    
    BufferedImage image = new BufferedImage(width, height,    
            BufferedImage.TYPE_INT_RGB);    
       
    Graphics g = image.getGraphics();    
    
    Random random = new Random();    
 
    g.setColor(getRandColor(200, 250));    
    g.fillRect(0, 0, width, height);    
    
    g.setFont(new Font("Times New Roman", Font.PLAIN, 18));     

    g.setColor(getRandColor(160, 200));    
    for (int i = 0; i < 100; i++) {    
        int x = random.nextInt(width);    
        int y = random.nextInt(height);    
        int xl = random.nextInt(12);    
        int yl = random.nextInt(12);    
        g.drawLine(x, y, x + xl, y + yl);    
    }    
 
    String sRand = "";    
    for (int i = 0; i < 4; i++) {    
        String rand = String.valueOf(random.nextInt(10));    
        sRand += rand;    

        g.setColor(new Color(20 + random.nextInt(110), 20 + random    
        .nextInt(110), 20 + random.nextInt(110)));
        g.drawString(rand, 13 * i + 6, 16);    
    }    

    session.setAttribute("code", sRand);    
    
    g.dispose();    

    ImageIO.write(image, "JPEG", response.getOutputStream());  

///以下代码保证输出不报错。

    out.clear();

    out=pageContext.pushBody();

 

 

%>

在你需要引入的地方：
<img border=0 src="image.jsp">

就可以了。。。