protected void Page_Load(object sender, EventArgs e)

{

// 生成验证码

string checkCode = RandLetter(4);

// 把新的验证码保存到Session中

Session["CheckCode"] = checkCode;

// 输入验证码

CreateImages(checkCode);

}

/// <summary>

/// 生成验证图片

/// </summary>

/// <param name="checkCode">验证字符</param>

private void CreateImages(string checkCode)

{

int iwidth = (int)(checkCode.Length * 13);

System.Drawing.Bitmap image = new System.Drawing.Bitmap(iwidth, 23);

Graphics g = Graphics.FromImage(image);

g.Clear(Color.White);

//定义颜色

Color[] c = { Color.Black, Color.Red, Color.DarkBlue, Color.Green, Color.Orange, Color.Brown, Color.DarkCyan, Color.Purple };

//定义字体

string[] font = { "Verdana", "Microsoft Sans Serif", "Comic Sans MS", "Arial", "宋体" };

Random rand = new Random();

//随机输出噪点

for (int i = 0; i < 50; i++)

{

int x = rand.Next(image.Width);

int y = rand.Next(image.Height);

g.DrawRectangle(new Pen(Color.LightGray, 0), x, y, 1, 1);

}

//输出不同字体和颜色的验证码字符

for (int i = 0; i < checkCode.Length; i++)

{

int cindex = rand.Next(7);

int findex = rand.Next(5);

Font f = new System.Drawing.Font(font[findex], 10, System.Drawing.FontStyle.Bold);

Brush b = new System.Drawing.SolidBrush(c[cindex]);

int ii = 4;

if ((i + 1) % 2 == 0)

{

ii = 2;

}

g.DrawString(checkCode.Substring(i, 1), f, b, 3 + (i * 12), ii);

}

//画一个边框

g.DrawRectangle(new Pen(Color.Black, 0), 0, 0, image.Width - 1, image.Height - 1);

//输出到浏览器

System.IO.MemoryStream ms = new System.IO.MemoryStream();

image.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg);

HttpContext.Current.Response.ClearContent();

//Response.ClearContent();

HttpContext.Current.Response.ContentType = "image/Jpeg";

HttpContext.Current.Response.BinaryWrite(ms.ToArray());

g.Dispose();

image.Dispose();

}

/// <summary>

/// 生成随机的字母

/// </summary>

/// <param name="count">生成字母的个数</param>

/// <returns>生成的验证码</returns>

private string RandLetter(int count)

{

string allLetters = "0,1,2,3,4,5,6,7,8,9,A,B,C,D,E,F,G,H,I,J,K,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z";

string[] allChar = allLetters.Split(',');

string checkCode = "";

int temp = -1; //记录上次随机数值，尽量避免生产几个一样的随机数

//采用一个简单的算法以保证生成随机数的不同

Random rand = new Random();

for (int i = 1; i < count + 1; i++)

{

if (temp != -1)

{

rand = new Random(i * temp * unchecked((int)DateTime.Now.Ticks));

}

int t = rand.Next(allChar.Length);

temp = t;

checkCode += allChar[t];

}

return checkCode;

}