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));
}
private 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]
        };
}
private 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
        };
}
private 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)
{
    int 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);
    Bitmap image2d = new Bitmap(image2d_x, image2d_y);
    Color black = Color.Black;
    Color white = Color.White;
    using (Graphics g = Graphics.FromImage(image2d))
    {
      g.Clear(black);
      g.DrawString(captchaText, font, Brushes.White, 0, 0);
    }
    Random rnd = new Random();
    double[] 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));
    double[][] 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++)
      {
        int xc = x - image2d_x / 2;
        int zc = y - image2d_y / 2;
        double yc = -(double)(image2d.GetPixel(x, y).ToArgb() & 0xff) / 256 * 4;
        double[] xyz = new double[] { xc, yc, zc, 1 };
        xyz = vectorProduct(xyz, T);
        coord[count] = xyz;
        count++;
      }
    }
    int image3d_x = 256;
    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;
}

using System.Drawing;

Response.ContentType = "image/pjpeg";
Captcha.Generate("我就是3D内容").Save(Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg);