验证码图片生成（4位字母与数字结合）

RandomImage.aspx.cs： 

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 RandomImage : System.Web.UI.Page{ protected void Page_Load(object sender, EventArgs e) { //输出带有随机验证码的图片 CreateCheckCodeImage(this.GenerateCheckCode()); } /// <summary> /// 随机生成4位随机字符（0-9）(A-Z) /// </summary> /// <returns></returns> private string GenerateCheckCode() { //定义验证码长度 int CODELENGTH = 4; int number; string RandomCode = string.Empty; Random r = new Random(); for (int i = 0; i < CODELENGTH; i++) { number = r.Next(); //字符从0-9,A-Z中随机生成，对应的ASCII码分别为48-57,65-90 number %= 36; if (number < 10) { number += 48; } else { number += 55; } RandomCode += ((char)number).ToString(); } //在Cookie中保存验证码 //Response.Cookies.Add(new HttpCookie("CheckCode",RandomCode)); Session["CheckCode"] = RandomCode; return RandomCode; } /// <summary> /// 输出包括4位随机数字的图片 /// </summary> /// <param name="CheckCode"></param> private void CreateCheckCodeImage(string CheckCode) { //若验证码为空，则直接返回 if (CheckCode == null || CheckCode.Trim() == string.Empty) { return; } //根据验证码的长度确定输出图片的宽度 int iWidth = (int)Math.Ceiling(CheckCode.Length*15m); int iHeight = 20; //创建图像 Bitmap image = new Bitmap(iWidth, iHeight); //从图像获取一个绘图面 Graphics g = Graphics.FromImage(image); try { Random r = new Random(); //清空图片背景色 g.Clear(Color.White); //画图片的背景噪音线10条 for (int i = 0; i < 10; i++) { int x1 = r.Next(image.Width); int x2 = r.Next(image.Width); int y1 = r.Next(image.Height); int y2 = r.Next(image.Height); //用银色画出噪音线 g.DrawLine(new Pen(Color.Silver), x1, x2, y1, y2); } //画图片的前景噪音点50个 for (int i = 0; i < 50; i++) { int x = r.Next(image.Width); int y = r.Next(image.Height); image.SetPixel(x, y, Color.FromArgb(r.Next())); } //画图片的框线 g.DrawRectangle(new Pen(Color.SaddleBrown), 0, 0, image.Width - 1, image.Height - 1); //定义绘制文字的字体 Font f = new Font("Arial", 12, (FontStyle.Bold | FontStyle.Italic)); //线性渐变画刷 System.Drawing.Drawing2D.LinearGradientBrush brush = new System.Drawing.Drawing2D.LinearGradientBrush(new Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.Purple, 1.2f, true); g.DrawString(CheckCode, f, brush, 2, 2); //创建内存流用于输出图片 using (System.IO.MemoryStream ms = new System.IO.MemoryStream()) { //图片格式制定为png image.Save(ms, System.Drawing.Imaging.ImageFormat.Png); //清除缓冲区流中的所有输出 Response.ClearContent(); //输出流的HTTP MIME类型设置为“image/Png” Response.ContentType = "image/Png"; //输出图片的二进制流 Response.BinaryWrite(ms.ToArray()); } } finally { //释放Bitmap对象和Graphics对象 g.Dispose(); image.Dispose(); } }}     

index.aspx：

<img src="RandomImage.aspx" alt="验证码" id="imgRandom" />