Generate Random Captcha

In many situations, you will need to generate a random captcha to distinguish between humans or robots. For example, it's naturaly to have a captcha when new user register an account. It's luck that python is very suitable for doing that.
                                         —— Graycat

Preparation

Env & OS

The following configuration is suitable for me but not necessary for you. After all, it's important to make a decision which is suitable for yourself.

Key	Value
Environment	Python2.7
Operating System	Ubuntu-LTS-16.04 X64

Dependence

Install python-pip and Pillow if you don't have it.

$ sudo apt install python-pip
$ pip install Pillow            # If your system is 32-bit, `PIL` is available,  if not, you'll use `Pillow` instead of `PIL`

Font File

Install font file, take consola as an example.
Download suitable font file from here to linux.

$ unzip YaHei.Consolas.1.12.zip                                     # unzip font file
$ mv YaHei.Consolas.1.12.ttf consola.ttf

You can add it to the system font file and activate it, even if this is not necessary for this program.

$ sudo mkdir /usr/share/fonts/consola/                              # make folder for font file
$ sudo cp Fonts/consola.ttf /usr/share/fonts/consola/
$ cd /usr/share/fonts/consola/
$ sudo mkfontscale && sudo mkfontdir && sudo fc-cache -fv           # activate font file

Operation

New File

$ mkdir /home/user/GenerateRandomCaptcha/
$ cd /home/user/GenerateRandomCaptcha/
$ vim captcha.py

Import Package

from PIL import Image, ImageDraw, ImageFont
import random
import string

FONT_FILE = 'Fonts/consola.ttf'

Class & Func

Self-define a class used to generate the exception we need.

class SimpleCaptchaException(Exception):  # Just a simple template that self define Exception class
    pass

Self-define a class of captcha include some necessary functions.

class SimpleCaptcha(object):
    def __init__(self, textLength=7, imgSize=(320, 180), fontSize=64, randomText=True, randomBgcolor=True):
        self.imgSize = imgSize
        self.text = "CAPTCHA"
        self.fontSize = fontSize
        self.bgColor = 255
        self.textLength = textLength
        self.image = None  # Current captcha image

        if randomText:
            self.text = self.getRandomText()
        if not self.text:
            raise SimpleCaptchaException("Field text must not be empty.")
        if not self.imgSize:
            raise SimpleCaptchaException("Image size must not be empty.")
        if not self.fontSize:
            raise SimpleCaptchaException("Font size must be defined.")
        if randomBgcolor:
            self.bgColor = self.getRandomColor()

    def getCenterCoords(self, draw, font):
        width, height = draw.textsize(self.text, font)
        xy = (self.imgSize[0] - width) / 2., (self.imgSize[1] - height) / 2.
        return xy

    def addNoiseDots(self, draw):
        size = self.image.size
        for item in range(int(size[0] * size[1] * 0.1)):
            draw.point((random.randint(0, size[0]), random.randint(0, size[1])), fill="white")
        return draw

    def addNoiseLines(self, draw):
        size = self.image.size
        width = None
        for item in range(8):
            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="white", width=width)
        for item in range(8):
            start = (-50, -50)
            end = (size[0] + 10, random.randint(0, size[1] + 10))
            draw.arc(start + end, 0, 360, fill="white")
        return draw

    def getCaptcha(self, imgSize=None, text=None, bgColor=None):
        if text is not None:
            self.text = text
        if imgSize is not None:
            self.imgSize = imgSize
        if bgColor is not None:
            self.bgColor = bgColor
        self.image = Image.new('RGB', self.imgSize, self.bgColor)  # Create image by instance a class called Image
        # Note that the font file must be present
        # or point to your OS's system font
        # Ex. on Mac the path should be '/Library/Fonts/Tahoma.ttf'
        # Ex. on Windows the path should be 'C:/Windows/Fonts/consola.ttf'
        font = ImageFont.truetype(FONT_FILE, self.fontSize)
        draw = ImageDraw.Draw(self.image)
        centerCoords = self.getCenterCoords(draw, font)
        draw.text(xy=centerCoords, text=self.text, font=font)
        draw = self.addNoiseDots(draw)  # Add some dot noise
        draw = self.addNoiseLines(draw)  # Add some random lines
        self.image.show()
        return self.image, self.text

    def getRandomText(self):
        text = string.lowercase + string.uppercase + string.digits  # Text of captcha include letter and number is natural
        random_text = ""
        for item in range(self.textLength):
            random_text += random.choice(text)
        return random_text

    def getRandomColor(self):
        r = random.randint(0, 255)
        g = random.randint(0, 255)
        b = random.randint(0, 255)
        return (r, g, b)

Main Func

Generate a entrance for program.

if __name__ == "__main__":
    counter = 0
    print '[*] Aim: get 7 consecutive successes.'
    while (True):
        sc = SimpleCaptcha()
        (image, text) = sc.getCaptcha()
        typeText = raw_input('[' + str(counter + 1) + '] Type words what you see: ')
        if not typeText.lower() == text.lower():
            counter = 0
            print '[*] False\n[*] Text: ' + text
        else:
            counter = counter + 1
            print '[*] True'

        if counter == 7:
            break
    print '[*] Congratulate that you have a good pair of eyes!'

Result

Conclusion

As well konwn, captcha includeing lower case, upper case and number is normal. And case of typing is ignored is default is also natural.
The above is my biggest change to the program, other little change includes name of method and main method.
That's all. Thanks.