类似于Google的扭曲验证码

using System;
using System.Drawing;
using System.IO;
using System.Text;

public partial class MyBlog_ValiImage : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        CreateCheckCodeImage(NextCheckCode(), this.Response);
    }
    /// <summary>
    /// 正弦曲线Wave扭曲图片
    /// </summary>
    /// <param name="srcBmp">图片路径</param>
    /// <param name="bXDir">如果扭曲则选择为True</param>
    /// <param name="nMultValue">波形的幅度倍数，越大扭曲的程度越高，一般为3</param>
    /// <param name="dPhase">波形的起始相位，取值区间[0-2*PI)</param>
    /// <returns></returns>
    public Bitmap TwistImage(Bitmap srcBmp, bool bXDir, double dMultValue, double dPhase)
    {
        Bitmap destBmp = new Bitmap(srcBmp.Width, srcBmp.Height);

        // 将位图背景填充为白色
        Graphics graph = Graphics.FromImage(destBmp);
        graph.FillRectangle(new SolidBrush(ColorTranslator.FromHtml("#f0f0f0")), 0, 0, destBmp.Width, destBmp.Height);
        graph.Dispose();

        double dBaseAxisLen = bXDir ? (double)destBmp.Height : (double)destBmp.Width;

        for (int i = 0; i < destBmp.Width; i++)
        {
            for (int j = 0; j < destBmp.Height; j++)
            {
                double dx = 0;
                dx = bXDir ? (Math.PI * (double)j) / dBaseAxisLen : (Math.PI * (double)i) / dBaseAxisLen;
                dx += dPhase;
                double dy = Math.Sin(dx);

                // 取得当前点的颜色
                int nOldX = 0, nOldY = 0;
                nOldX = bXDir ? i + (int)(dy * dMultValue) : i;
                nOldY = bXDir ? j : j + (int)(dy * dMultValue);

                Color color = srcBmp.GetPixel(i, j);
                if (nOldX >= 0 && nOldX < destBmp.Width
                && nOldY >= 0 && nOldY < destBmp.Height)
                {
                    destBmp.SetPixel(nOldX, nOldY, color);
                }
            }
        }
        try
        {
            srcBmp.Dispose();
        }
        catch { };
        return destBmp;
    }
    /// <summary>
    /// 生成验证码图片
    /// </summary>
    /// <param name="checkCode"></param>
    /// <param name="response"></param>
    public void CreateCheckCodeImage(string checkCode, System.Web.HttpResponse response)
    {
        int width = 120;//验证码图片宽度
        int height = 24;//验证码图片高度
        Font font = new Font("Arial", 17, FontStyle.Bold);//验证码字体

        SolidBrush brush = new SolidBrush(Color.Blue);//用于写验证码的画笔

        Bitmap image = new Bitmap(width, height);//生成图像

        Graphics g = Graphics.FromImage(image);//生成一个绘画面板（画布）

        g.Clear(ColorTranslator.FromHtml("#f0f0f0"));//用指定颜色填充画布

        RectangleF rect = new RectangleF(10, 0, width, height);//定义文字的绘制矩形

        g.DrawString(checkCode, font, brush, rect);//将验证码写到画布上
        System.IO.MemoryStream ms = new System.IO.MemoryStream();

        image = TwistImage(image, true, rnd(), rnd());

        try
        {
            image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif);
            response.ClearContent();
            response.ContentType = "image/Gif";
            response.BinaryWrite(ms.ToArray());
        }
        finally
        {
            ms.Flush();
            ms.Close();
            ms.Dispose();
            g.Dispose();
            image.Dispose();
        }
    }
    public string NextCheckCode(int codeCount)
    {
        string[] allChar = new string[] { "A", "B", "C", "D", "E", "F", "G", "H", "I", "J", " K", "L", "M", "N", "O", "P", "Q", "R", "S", "T", "U", "W", " X", "Y", "Z " };
        Random rnd = new Random((int)DateTime.Now.Ticks);
        StringBuilder code = new StringBuilder();
        for (int i = 0; i < codeCount; i++)
        {
            code.Append(allChar[rnd.Next(0, 25)]);
        }
        return code.ToString().Replace(" ", "");
    }
    /// <summary>
    /// 生成5位随机英文字母
    /// </summary>
    /// <returns></returns>
    public string NextCheckCode()
    {
        return NextCheckCode(5);
    }
    public int rnd()
    {
        Random rnd = new Random((int)DateTime.Now.Ticks);

        if (rnd.Next(0, 1) == 1)
        {
            return rnd.Next(5, 15);
        }
        else
        {
            return rnd.Next(-15, -5);
        }
    }
}