web 图片验证码 验证

做一个图片验证码 界面中的代码

        验证码：<asp:TextBox ID="TextBox1" runat="server"></asp:TextBox><asp:Image ID="Image1" ImageUrl="YZM.aspx" runat="server" />
        <asp:Button ID="Button1" runat="server" Text="验证" /><asp:Label ID="Label1" runat="server" Text=""></asp:Label>
    

image控件指向YZM.aspx

<asp:Image ID="Image1" ImageUrl="YZM.aspx" runat="server" />

创建YZM.aspx在后台把验证码画出来代码如下

//引用  using System.Drawing  命名空间

        // 创建画布
        Bitmap map = new Bitmap(100, 50);
        //指定在那个画布上绘制
        Graphics g = Graphics.FromImage(map);
        //随机数类
        Random r = new Random();
        //绘制背景色

        //准备好背景颜色放入集合中去
        List<Color> clist = new List<Color>();
        clist.Add(Color.Azure);
        clist.Add(Color.LightGray);
        clist.Add(Color.CornflowerBlue);
        clist.Add(Color.SlateBlue);
        clist.Add(Color.MediumBlue);
        clist.Add(Color.SteelBlue);
        clist.Add(Color.DarkGreen);
        clist.Add(Color.GreenYellow);
        clist.Add(Color.SlateBlue);
        //绘制背景颜色
        g.FillRectangle(new SolidBrush(clist[r.Next(0, clist.Count)]), 0, 0, 100, 50);
         
       //绘制干扰线
        for(int i =0 ;i<10;i++)//循环绘制I条干扰线
        {
         //创建 Pen 对象 pen
        Pen pen= new Pen(new SolidBrush(clist[r.Next(0, clist.Count)]),r.Next(0,10));
        //绘制干扰线 
        g.DrawLine(pen, r.Next(0, 100), r.Next(0, 50), r.Next(0, 100), r.Next(0, 50));
        }
        //验证码绘制内容
        string ss = "ABCDEFHIJKLMNOPQRSTUVWXYZabxdefghijklmnopqrstuvwxyz1234567890";
        string s = "";
        for (int i = 0; i < 4; i++)//随机出四位验证码
        {
            s += ss.Substring((r.Next(0, ss.Length)), 1);
        }
        Session["yzm"] = s;
        //绘制的字体
        Font f = new Font("黑体", 30);
        //绘制的画刷
        Brush b = new SolidBrush(Color.Brown);
        //开始绘制验证码
        g.DrawString(s, f, b, 0, 0);

        //保存绘制的验证码
        //Response.OutputStream输出流
        //System.Drawing.Imaging.ImageFormat.Jpeg 保存的格式
        map.Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);
        Response.End();

页面显示

验证验证码方法

//注册验证按钮点击事件
Button1.Click += Button1_Click;
   
 void Button1_Click(object sender, EventArgs e)
    {
        string t1 = TextBox1.Text;
        string t2 = Session["YZM"].ToString();

        if (t1.ToUpper() == t2.ToUpper())
        {
            Label1.Text = "验证成功！";
        }
        else
        {
            Label1.Text = "验证失败！";
        }
    } 

看不清除点击图片更换验证码 用js 方法

<script type="text/javascript">
    var a = 0;
    document.getElementById("Image1").onclick = function () {
        this.setAttribute("src", "yzm.aspx?id=" + a);
        a++;
    }
</script>