Captcha generating script by Neil Harris

with some tweaks for command-line options
Requires Python Imaging Library, a word list file, and a TrueType font.

captcha.py

@@ -0,0 +1,154 @@
+#!/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.,
+# 59 Temple Place - Suite 330, Boston, MA 02111-1307, 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
+
+import random
+import Image
+import ImageFont
+import ImageDraw
+import ImageEnhance
+import ImageOps
+import math, string, md5
+import getopt
+import os
+import sys
+
+# 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(-30, 30) # 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:
+		print "whoops"
+		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 = 3
+	wob = 0.20*dim[1]/k
+	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))
+	# and turn into black on white
+	im = ImageOps.invert(im)
+		
+	# save the image, in format determined from filename
+	im.save(file_name)
+
+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.
+	"""
+	font = "VeraBd.ttf"
+	wordlist = "awordlist.txt"
+	key = "CHANGE_THIS_SECRET!"
+	output = "."
+	count = 20
+	fill = 0
+	verbose = False
+	
+	opts, args = getopt.getopt(sys.argv[1:], "", ["font=", "wordlist=", "key=", "output=", "count=", "fill=", "verbose"])
+	for o, a in opts:
+		if o == "--font":
+			font = a
+		if o == "--wordlist":
+			wordlist = a
+		if o == "--key":
+			key = a
+		if o == "--output":
+			output = a
+		if o == "--count":
+			count = int(a)
+		if o == "--fill":
+			fill = int(a)
+		if o == "--verbose":
+			verbose = True
+	
+	if fill:
+		# Option processing order is not guaranteed, so count the output
+		# files after...
+		count = max(0, fill - len(os.listdir(output)))
+	
+	words = [string.lower(x.strip()) for x in open(wordlist).readlines()]
+	words = [x for x in words
+		if len(x) <= 5 and len(x) >= 4 and x[0] != "f"
+		and x[0] != x[1] and x[-1] != x[-2]
+		and (not "'" in x)]
+	for i in range(count):
+		word1 = words[random.randint(0,len(words)-1)]
+		word2 = words[random.randint(0,len(words)-1)]
+		word = word1+word2
+		salt = "%08x" % random.randrange(2**32)
+		# 64 bits of hash is plenty for this purpose
+		hash = md5.new(key+salt+word+key+salt).hexdigest()[:16]
+		filename = "image_%s_%s.png" % (salt, hash)
+		if verbose:
+			print filename
+		gen_captcha(word, font, 40, os.path.join(output, filename))