captcha.py

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#!/usr/bin/python
#
# Script to generate distorted text images for a captcha system.
#
# Copyright (C) 2005 Neil Harris
#
# This program is free software; you can redistribute it and/or modify
# it under the terms of the GNU General Public License as published by
# the Free Software Foundation; either version 2 of the License, or
# (at your option) any later version.
#
# This program is distributed in the hope that it will be useful,
# but WITHOUT ANY WARRANTY; without even the implied warranty of
# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
# GNU General Public License for more details.
#
# You should have received a copy of the GNU General Public License along
# with this program; if not, write to the Free Software Foundation, Inc.,
# 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
# http://www.gnu.org/copyleft/gpl.html
#
# Further tweaks by Brion Vibber <brion@pobox.com>:
# 2006-01-26: Add command-line options for the various parameters
# 2007-02-19: Add --dirs param for hash subdirectory splits
# Tweaks by Greg Sabino Mullane <greg@turnstep.com>:
# 2008-01-06: Add regex check to skip words containing other than a-z
 
import random
import math
import hashlib
from optparse import OptionParser
import os
import sys
import re
 
try:
    from PIL import Image
    from PIL import ImageFont
    from PIL import ImageDraw
    from PIL import ImageEnhance
    from PIL import ImageOps
    from PIL import ImageMath
except:
    sys.exit("This script requires the Python Imaging Library - http://www.pythonware.com/products/pil/")
 
nonalpha = re.compile('[^a-z]') # regex to test for suitability of words
 
# Does X-axis wobbly copy, sandwiched between two rotates
def wobbly_copy(src, wob, col, scale, ang):
    x, y = src.size
    f = random.uniform(4*scale, 5*scale)
    p = random.uniform(0, math.pi*2)
    rr = ang+random.uniform(-10, 10) # vary, but not too much
    int_d = Image.new('RGB', src.size, 0) # a black rectangle
    rot = src.rotate(rr, Image.BILINEAR)
    # Do a cheap bounding-box op here to try to limit work below
    bbx = rot.getbbox()
    if bbx == None:
        return src
    else:
        l, t, r, b= bbx
    # and only do lines with content on
    for i in range(t, b+1):
        # Drop a scan line in
        xoff = int(math.sin(p+(i*f/y))*wob)
        xoff += int(random.uniform(-wob*0.5, wob*0.5))
        int_d.paste(rot.crop((0, i, x, i+1)), (xoff, i))
    # try to stop blurring from building up
    int_d = int_d.rotate(-rr, Image.BILINEAR)
    enh = ImageEnhance.Sharpness(int_d)
    return enh.enhance(2)
 
 
def gen_captcha(text, fontname, fontsize, file_name):
    """Generate a captcha image"""
    # white text on a black background
    bgcolor = 0x0
    fgcolor = 0xffffff
    # create a font object
    font = ImageFont.truetype(fontname,fontsize)
    # determine dimensions of the text
    dim = font.getsize(text)
    # create a new image significantly larger that the text
    edge = max(dim[0], dim[1]) + 2*min(dim[0], dim[1])
    im = Image.new('RGB', (edge, edge), bgcolor)
    d = ImageDraw.Draw(im)
    x, y = im.size
    # add the text to the image
    d.text((x/2-dim[0]/2, y/2-dim[1]/2), text, font=font, fill=fgcolor)
    k = 2
    wob = 0.09*dim[1]
    rot = 45
    # Apply lots of small stirring operations, rather than a few large ones
    # in order to get some uniformity of treatment, whilst
    # maintaining randomness
    for i in range(k):
        im = wobbly_copy(im, wob, bgcolor, i*2+3, rot+0)
        im = wobbly_copy(im, wob, bgcolor, i*2+1, rot+45)
        im = wobbly_copy(im, wob, bgcolor, i*2+2, rot+90)
        rot += 30
 
    # now get the bounding box of the nonzero parts of the image
    bbox = im.getbbox()
    bord = min(dim[0], dim[1])/4 # a bit of a border
    im = im.crop((bbox[0]-bord, bbox[1]-bord, bbox[2]+bord, bbox[3]+bord))
 
    # Create noise
    nblock = 4
    nsize = (im.size[0] / nblock, im.size[1] / nblock)
    noise = Image.new('L', nsize, bgcolor)
    data = noise.load()
    for x in range(nsize[0]):
        for y in range(nsize[1]):
            r = random.randint(0, 65)
            gradient = 70 * x / nsize[0]
            data[x, y] = r + gradient
    # Turn speckles into blobs
    noise = noise.resize(im.size, Image.BILINEAR)
    # Add to the image
    im = ImageMath.eval('convert(convert(a, "L") / 3 + b, "RGB")', a=im, b=noise)
 
    # and turn into black on white
    im = ImageOps.invert(im)
 
    # save the image, in format determined from filename
    im.save(file_name)
 
def gen_subdir(basedir, md5hash, levels):
    """Generate a subdirectory path out of the first _levels_
    characters of _hash_, and ensure the directories exist
    under _basedir_."""
    subdir = None
    for i in range(0, levels):
        char = md5hash[i]
        if subdir:
            subdir = os.path.join(subdir, char)
        else:
            subdir = char
        fulldir = os.path.join(basedir, subdir)
        if not os.path.exists(fulldir):
            os.mkdir(fulldir)
    return subdir
 
def try_pick_word(words, blacklist, verbose, nwords, min_length, max_length):
    if words is not None:
        word = words[random.randint(0,len(words)-1)]
        while nwords > 1:
            word2 = words[random.randint(0,len(words)-1)]
            word = word + word2
            nwords = nwords - 1
    else:
        word = ''
        max_length = max_length if max_length > 0 else 10
        for i in range(0, random.randint(min_length, max_length)):
            word = word + chr(97 + random.randint(0,25))
 
    if verbose:
        print("word is %s" % word)
 
    if len(word) < min_length:
        if verbose:
            print("skipping word pair '%s' because it has fewer than %d characters" % (word, min_length))
        return None
 
    if max_length > 0 and len(word) > max_length:
        if verbose:
            print("skipping word pair '%s' because it has more than %d characters" % (word, max_length))
        return None
 
    if nonalpha.search(word):
        if verbose:
            print("skipping word pair '%s' because it contains non-alphabetic characters" % word)
        return None
 
    for naughty in blacklist:
        if naughty in word:
            if verbose:
                print("skipping word pair '%s' because it contains blacklisted word '%s'" % (word, naughty))
            return None
    return word
 
def pick_word(words, blacklist, verbose, nwords, min_length, max_length):
    for x in range(1000): # If we can't find a valid combination in 1000 tries, just give up
        word = try_pick_word(words, blacklist, verbose, nwords, min_length, max_length)
        if word:
            return word
    sys.exit("Unable to find valid word combinations")
 
def read_wordlist(filename):
    f = open(filename)
    words = [x.strip().lower() for x in f.readlines()]
    f.close()
    return words
 
if __name__ == '__main__':
    """This grabs random words from the dictionary 'words' (one
    word per line) and generates a captcha image for each one,
    with a keyed salted hash of the correct answer in the filename.
 
    To check a reply, hash it in the same way with the same salt and
    secret key, then compare with the hash value given.
    """
    script_dir = os.path.dirname(os.path.realpath(__file__))
    parser = OptionParser()
    parser.add_option("--wordlist", help="A list of words (required)", metavar="WORDS.txt")
    parser.add_option("--random", help="Use random charcters instead of a wordlist", action="store_true")
    parser.add_option("--key", help="The passphrase set as $wgCaptchaSecret (required)", metavar="KEY")
    parser.add_option("--output", help="The directory to put the images in - $wgCaptchaDirectory (required)", metavar="DIR")
    parser.add_option("--font", help="The font to use (required)", metavar="FONT.ttf")
    parser.add_option("--font-size", help="The font size (default 40)", metavar="N", type='int', default=40)
    parser.add_option("--count", help="The maximum number of images to make (default 20)", metavar="N", type='int', default=20)
    parser.add_option("--blacklist", help="A blacklist of words that should not be used", metavar="FILE", default=os.path.join(script_dir, "blacklist"))
    parser.add_option("--fill", help="Fill the output directory to contain N files, overrides count, cannot be used with --dirs", metavar="N", type='int')
    parser.add_option("--dirs", help="Put the images into subdirectories N levels deep - $wgCaptchaDirectoryLevels", metavar="N", type='int')
    parser.add_option("--verbose", "-v", help="Show debugging information", action='store_true')
    parser.add_option("--number-words", help="Number of words from the wordlist which make a captcha challenge (default 2)", type='int', default=2)
    parser.add_option("--min-length", help="Minimum length for a captcha challenge", type='int', default=1)
    parser.add_option("--max-length", help="Maximum length for a captcha challenge", type='int', default=-1)
 
    opts, args = parser.parse_args()
 
    if opts.wordlist:
        wordlist = opts.wordlist
    elif opts.random:
        wordlist = None
    else:
        sys.exit("Need to specify a wordlist")
    if opts.key:
        key = opts.key
    else:
        sys.exit("Need to specify a key")
    if opts.output:
        output = opts.output
    else:
        sys.exit("Need to specify an output directory")
    if opts.font and os.path.exists(opts.font):
        font = opts.font
    else:
        sys.exit("Need to specify the location of a font")
 
    blacklist = read_wordlist(opts.blacklist)
    count = opts.count
    fill = opts.fill
    dirs = opts.dirs
    verbose = opts.verbose
    fontsize = opts.font_size
 
    if fill:
        count = max(0, fill - len(os.listdir(output)))
 
    words = None
    if wordlist:
        words = read_wordlist(wordlist)
        words = [x for x in words
            if len(x) in (4,5) and x[0] != "f"
            and x[0] != x[1] and x[-1] != x[-2]]
 
    for i in range(count):
        word = pick_word(words, blacklist, verbose, opts.number_words, opts.min_length, opts.max_length)
        salt = "%08x" % random.randrange(2**32)
        # 64 bits of hash is plenty for this purpose
        md5hash = hashlib.md5((key+salt+word+key+salt).encode('utf-8')).hexdigest()[:16]
        filename = "image_%s_%s.png" % (salt, md5hash)
        if dirs:
            subdir = gen_subdir(output, md5hash, dirs)
            filename = os.path.join(subdir, filename)
        if verbose:
            print(filename)
        gen_captcha(word, font, fontsize, os.path.join(output, filename))