本技术来源：

3DCaptcha http://www-personal.umich.edu/~mressl/3dcaptcha/

下载地址 http://code.google.com/p/3dcaptcha/

官方LOGO

本例完全由此样例程序翻译而来,未作任何附加处理.

以下是C#对此算法的实现

/** 3DCaptcha for .net* * http://www-personal.umich.edu/~mressl/3dcaptcha/     (php)* http://code.google.com/p/3dcaptcha/                  (php)* * Translate :  Aimeast* Blog      :  http://www.cnblogs.com/Aimeast/*/using System;
using System.Drawing;namespace Captcha
{public static class Captcha{private static double[] addVector(double[] a, double[] b){return new double[] { a[0] + b[0], a[1] + b[1], a[2] + b[2] };}private static double[] scalarProduct(double[] vector, double scalar){return new double[] { vector[0] * scalar, vector[1] * scalar, vector[2] * scalar };}private static double dotProduct(double[] a, double[] b){return a[0] * b[0] + a[1] * b[1] + a[2] * b[2];}private static double norm(double[] vector){return Math.Sqrt(dotProduct(vector, vector));}private static double[] normalize(double[] vector){return scalarProduct(vector, 1.0 / norm(vector));}// http://en.wikipedia.org/wiki/Cross_productprivate static double[] crossProduct(double[] a, double[] b){return new double[] {(a[1] * b[2] - a[2] * b[1]),(a[2] * b[0] - a[0] * b[2]),(a[0] * b[1] - a[1] * b[0])};}private static double[] vectorProductIndexed(double[] v, double[] m, int i){return new double[]{v[i + 0] * m[0] + v[i + 1] * m[4] + v[i + 2] * m[8] + v[i + 3] * m[12],v[i + 0] * m[1] + v[i + 1] * m[5] + v[i + 2] * m[9] + v[i + 3] * m[13],v[i + 0] * m[2] + v[i + 1] * m[6] + v[i + 2] * m[10]+ v[i + 3] * m[14],v[i + 0] * m[3] + v[i + 1] * m[7] + v[i + 2] * m[11]+ v[i + 3] * m[15]};}private static double[] vectorProduct(double[] v, double[] m){return vectorProductIndexed(v, m, 0);}private static double[] matrixProduct(double[] a, double[] b){double[] o1 = vectorProductIndexed(a, b, 0);double[] o2 = vectorProductIndexed(a, b, 4);double[] o3 = vectorProductIndexed(a, b, 8);double[] o4 = vectorProductIndexed(a, b, 12);return new double[]{o1[0], o1[1], o1[2], o1[3],o2[0], o2[1], o2[2], o2[3],o3[0], o3[1], o3[2], o3[3],o4[0], o4[1], o4[2], o4[3]};}// http://graphics.idav.ucdavis.edu/education/GraphicsNotes/Camera-Transform/Camera-Transform.htmlprivate static double[] cameraTransform(double[] C, double[] A){double[] w = normalize(addVector(C, scalarProduct(A, -1)));double[] y = new double[] { 0, 1, 0 };double[] u = normalize(crossProduct(y, w));double[] v = crossProduct(w, u);double[] t = scalarProduct(C, -1);return new double[]{u[0], v[0], w[0], 0,u[1], v[1], w[1], 0,u[2], v[2], w[2], 0,dotProduct(u, t), dotProduct(v, t), dotProduct(w, t), 1};}// http://graphics.idav.ucdavis.edu/education/GraphicsNotes/Viewing-Transformation/Viewing-Transformation.htmlprivate static double[] viewingTransform(double fov, double n, double f){fov *= (Math.PI / 180);double cot = 1.0 / Math.Tan(fov / 2);return new double[]{cot,   0,      0,      0,0,        cot,    0,      0, 0,       0,      (f + n) / (f - n),     -1,0,       0,      2 * f * n / (f - n),    0};}public static Image Generate(string captchaText){Random rnd = new Random();// 3dcha parametersint fontsize = 24;Font font = new Font("Arial", fontsize);SizeF sizeF;using (Graphics g = Graphics.FromImage(new Bitmap(1, 1))){sizeF = g.MeasureString(captchaText, font, 0, StringFormat.GenericDefault);}int image2d_x = (int)sizeF.Width;int image2d_y = (int)(fontsize * 1.3);double bevel = 4;// Create 2d imageBitmap image2d = new Bitmap(image2d_x, image2d_y);Color black = Color.Black;Color white = Color.White;// Paint 2d imageusing (Graphics g = Graphics.FromImage(image2d)){g.Clear(black);g.DrawString(captchaText, font, Brushes.White, 0, 0);}// Calculate projection matrixdouble[] T = cameraTransform(new double[] { rnd.Next(-90, 90), -200, rnd.Next(150, 250) },new double[] { 0, 0, 0 });T = matrixProduct(T,viewingTransform(60, 300, 3000));// Calculate coordinatesdouble[][] coord = new double[image2d_x * image2d_y][];int count = 0;for (int y = 0; y < image2d_y; y += 2){for (int x = 0; x < image2d_x; x++){// calculate x1, y1, x2, y2int xc = x - image2d_x / 2;int zc = y - image2d_y / 2;double yc = -(double)(image2d.GetPixel(x, y).ToArgb() & 0xff) / 256 * bevel;double[] xyz = new double[] { xc, yc, zc, 1 };xyz = vectorProduct(xyz, T);coord[count] = xyz;count++;}}// Create 3d imageint image3d_x = 256;//$image3d_y = $image3d_x / 1.618;int image3d_y = image3d_x * 9 / 16;Bitmap image3d = new Bitmap(image3d_x, image3d_y);Color fgcolor = Color.White;Color bgcolor = Color.Black;using (Graphics g = Graphics.FromImage(image3d)){g.Clear(bgcolor);count = 0;double scale = 1.75 - (double)image2d_x / 400;for (int y = 0; y < image2d_y; y += 2){for (int x = 0; x < image2d_x; x++){if (x > 0){double x0 = coord[count - 1][0] * scale + image3d_x / 2;double y0 = coord[count - 1][1] * scale + image3d_y / 2;double x1 = coord[count][0] * scale + image3d_x / 2;double y1 = coord[count][1] * scale + image3d_y / 2;g.DrawLine(new Pen(fgcolor), (float)x0, (float)y0, (float)x1, (float)y1);}count++;}}}return image3d;}}
}

使用方法

this.BackgroundImage = Captcha.Generate("Code");

效果截图