后臺文件:

 1using system;
 2using system.data;
 3using system.configuration;
 4using system.collections;
 5using system.drawing;
 6using system.web;
 7using system.web.security;
 8using system.web.ui;
 9using system.web.ui.webcontrols;
10using system.web.ui.webcontrols.webparts;
11using system.web.ui.htmlcontrols;
12
13public partial class default2 : system.web.ui.page
14{
15    protected void page_load(object sender, eventargs e)
16    {
17        if(!this.ispostback)
18        {
19            this.genimg(this.gencode(4));
20        }
21
22    }
23    //產(chǎn)生隨機(jī)字符串
24    private string gencode(int num)
25    {
26        string[] source={"0","1","2","3","4","5","6","7","8","9",
27                            "a","b","c","d","e","f","g","h","i","j","k","l","m","n",
28                            "o","p","q","r","s","t","u","v","w","x","y","z"};
29        string code="";
30        random rd=new random();
31        for(int i=0;i < num;i++)
32        {
33            code += source[rd.next(0,source.length)];
34        }
35        return code;
36    }
37
38        //生成圖片
39    private void genimg(string code)
40    {
41        bitmap mypalette = new bitmap(60, 20);//定義一個畫板
42
43        graphics gh = graphics.fromimage(mypalette);//在畫板上定義繪圖的實(shí)例
44
45        rectangle rc = new rectangle(0, 0, 60, 20);//定義一個矩形
46
47        gh.fillrectangle(new solidbrush(color.blue), rc);//填充矩形
48        gh.drawstring(code, new font("宋體", 16), new solidbrush(color.white), rc);//在矩形內(nèi)畫出字符串
49
50        mypalette.save(response.outputstream, system.drawing.imaging.imageformat.jpeg);//將圖片顯示出來
51
52        session["validatecode"] = code;//將字符串保存到session中，以便需要時進(jìn)行驗(yàn)證
53
54        gh.dispose();
55        mypalette.dispose();
56    }
57
58}

　　html文件:

　　加入一個html控件image即可

<%@ page language="c#" autoeventwireup="true" codefile="default2.aspx.cs" inherits="default2" %>
<img src="default2.aspx" />