请教一下，C#中如何实现 验证码功能，听说有个什么东西能自动画图的哟

using System;
using System.Data;
using System.Configuration;
using System.Collections;
using System.Web;
using System.Web.Security;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Web.UI.WebControls.WebParts;
using System.Web.UI.HtmlControls;
using System.Drawing;

public partial class ValidatePic : System.Web.UI.Page
{
protected void Page_Load(object sender, EventArgs e)
{
Random r = new Random();
Color MyColor = Color.FromArgb(r.Next(255), r.Next(255), r.Next(255));
Bitmap img = new Bitmap(150, 50);
Graphics g = Graphics.FromImage(img);
g.Clear(Color.Violet);
for (int i = 0; i < 4000; i++)
{
MyColor = Color.FromArgb(r.Next(255), r.Next(255), r.Next(255));
img.SetPixel(r.Next(150), r.Next(50), MyColor); //产生4000个随机颜色的杂点
}
SolidB