Generating a 3D CAPTCHA [pic]

Question

I would like to write a Python script that would generate a 3D CAPTCHA like this one:

Which graphics libraries can I use?

Source: ocr-research.org.ua

Answer 1

There are many approaches. I would personally create the image in Python Imaging Library using ImageDraw's draw.text, convert to a NumPy array (usint NumPy's asarray) then render with Matplotlib. (Requires Matplotlib maintenance package).

Full code (in 2.5):

import numpy, pylab
from PIL import Image, ImageDraw, ImageFont
import matplotlib.axes3d as axes3d

sz = (50,30)

img = Image.new('L', sz, 255)
drw = ImageDraw.Draw(img)
font = ImageFont.truetype("arial.ttf", 20)

drw.text((5,3), 'text', font=font)
img.save('c:/test.png')

X , Y = numpy.meshgrid(range(sz[0]),range(sz[1]))
Z = 1-numpy.asarray(img)/255

fig = pylab.figure()
ax = axes3d.Axes3D(fig)
ax.plot_wireframe(X, -Y, Z, rstride=1, cstride=1)
ax.set_zlim((0,50))
fig.savefig('c:/test2.png')

Obviously there's a little work to be done, eliminating axes, changing view angle, etc..

Answer 2

Another binding to consider for rendering with opengl is pyglet. Its best feature is that it is just one download. I think it contains everything you need to implement what Anurag spells out.

I will caution you that what you're trying to do is not exactly a simple first project in 3d graphics. If this is your first exposure to OpenGL, consider a series of tutorials like NeHe Tutorials and other help from the OpenGL website.

Answer 3

I'm not sure I would bother with a full 3D library for what you have above. Just generate a matrix of 3D points, generate the text with something like PIL, scan over it to find which points on the grid are raised, pick a random camera angle and then project the points into a 2D image and draw them with PIL to the final image.

That being said... you may be able to use VPython if you don't want to do the 3D math yourself.

Answer 4

Use Python bindings for OpenGL, http://pyopengl.sourceforge.net/.

Create a 2D image of white color text over a black surface using PIL. Make a 3D grid from this, increase z of point where color is white, maybe set z=color value, so by blurring the image you can get real curves in the z direction.

Create an OpenGL triangle from these points, use wireframe mode while rendering.

Grab the OpenGL buffer into an image, for example, http://python-opengl-examples.blogspot.com/2009/04/render-to-texture.html.