Captcha implement with Python

captcha.py

# -*- coding: utf-8 -*-
from __future__ import absolute_import

from os import path
import random
import string
from StringIO import StringIO

from PIL import Image, ImageDraw, ImageFont, ImageFilter
from flask import make_response

PATH_DIR = path.dirname(path.abspath(__file__))


class Captcha(object):

    FONT_PATH = path.join(PATH_DIR, 'fonts/captcha.ttf')
    LETTERS = string.ascii_letters + string.digits

    def __init__(self, length=4, size=(120, 50), fontsize=36):
        self.size = size
        self.fontsize = fontsize
        self.length = length

    def _center_coords(self, draw, text, font):
        width, height = draw.textsize(text, font)
        xy = (self.size[0] - width) / 2.0, (self.size[1] - height) / 2.0
        return xy

    def _add_noise_dots(self, draw, image):
        """Add noise dots"""

        size = image.size
        for _ in range(int(size[0] * size[1] * 0.1)):
            xy = (random.randint(0, size[0]), random.randint(0, size[1]))
            draw.point(xy, fill=self._random_text_color())
        return draw

    def _add_noise_lines(self, draw, image):
        size = image.size
        line_color = self._random_bg_color()

        for _ in range(3):
            width = random.randint(1, 2)
            start = (0, random.randint(0, size[1] - 1))
            end = (size[0], random.randint(0, size[1] - 1))
            draw.line([start, end], fill=line_color, width=width)

        for _ in range(2):
            start = (-50, -50)
            end = (size[0] + 10, random.randint(0, size[1] + 10))
            draw.arc(start + end, 0, 360, fill=line_color)
        return draw

    def _random_text(self):
        return ''.join([random.choice(self.LETTERS) for _ in range(self.length)])

    def _random_color(self, range_min, range_max):
        r, g, b = (random.randint(range_min, range_max) for _ in range(3))
        return (r, g, b)

    def _random_bg_color(self):
        return self._random_color(200, 255)

    def _random_text_color(self):
        return self._random_color(0, 150)

    def get(self):
        """generate and return captcha"""
        image = Image.new("RGB", self.size, self._random_bg_color())
        font = ImageFont.truetype(self.FONT_PATH, self.fontsize)
        draw = ImageDraw.Draw(image)
        text = self._random_text()
        xy = self._center_coords(draw, text, font)
        draw.text(xy=xy, text=text, font=font, fill=self._random_text_color())

        # Add some dot noise
        draw = self._add_noise_dots(draw, image)

        # Add some random lines
        draw = self._add_noise_lines(draw, image)

        image = image.filter(ImageFilter.EDGE_ENHANCE_MORE)  # 滤镜，边界加强（阈值更大）
        return image, text.lower()


def make_image_response(img, content_type='image/jpeg'):
    assert isinstance(img, Image.Image)
    assert content_type.split('/')[0].lower() == 'image'

    img_type = content_type.split('/', 1)[1].upper()
    buff = StringIO()
    img.save(buff, img_type)
    response = make_response(buff.getvalue())
    response.headers['Content-Type'] = content_type
    return response