验证码图片生成（4位字母与数字结合）

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();
}
}
}