Captcha
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Transcript of Captcha
![Page 1: Captcha](https://reader036.fdocuments.us/reader036/viewer/2022082804/5490bb1fb479593e0a8b45b3/html5/thumbnails/1.jpg)
by jithin parakka
CAPTCHA
How it Works, How to create your own CAPTCHA
![Page 2: Captcha](https://reader036.fdocuments.us/reader036/viewer/2022082804/5490bb1fb479593e0a8b45b3/html5/thumbnails/2.jpg)
by jithin parakka
CAPTCHA
Completely Automated Public Turing test to tell Computers and Humans Apart
![Page 3: Captcha](https://reader036.fdocuments.us/reader036/viewer/2022082804/5490bb1fb479593e0a8b45b3/html5/thumbnails/3.jpg)
by jithin parakka
CAPTCHA
• You can see it in almost all signup form• It is used to verify that whether the party
who is filling the form is a human or a computer program instructed to do so
• The most common form of CAPTCHA is an image of several distorted letters
![Page 4: Captcha](https://reader036.fdocuments.us/reader036/viewer/2022082804/5490bb1fb479593e0a8b45b3/html5/thumbnails/4.jpg)
by jithin parakka
Interesting fact
• People who design the tests aren't always upset when their tests fail
• Because every CAPTCHA failure is really an advance in artificial intelligence.
![Page 5: Captcha](https://reader036.fdocuments.us/reader036/viewer/2022082804/5490bb1fb479593e0a8b45b3/html5/thumbnails/5.jpg)
by jithin parakka
CAPTCHA and Turing
• Is a reverse Turing test• it is administered by a machine and targeted
at a human• in contrast to the standard Turing test that is
typically administered by a human and targeted at a machine
![Page 6: Captcha](https://reader036.fdocuments.us/reader036/viewer/2022082804/5490bb1fb479593e0a8b45b3/html5/thumbnails/6.jpg)
by jithin parakka
Things to be taken care
• Your CAPTCHA image should not contain any metadata.
• Make modification to the text.• Don't use same CAPTCHA always.• One possible method to implement CAPTCHA
is to store a set of image and corresponding text in database and compare them.
• Another solution is create image on the fly.
![Page 7: Captcha](https://reader036.fdocuments.us/reader036/viewer/2022082804/5490bb1fb479593e0a8b45b3/html5/thumbnails/7.jpg)
by jithin parakka
How to create CAPTCHA
• Generate a random text– Here I am using md5 function to generate a random
text. I am using php microtime() function as input to md5 to make it random. Store this in session variable.
• Create an image using php ImageCreate() function
• Make the image very complex using functions available in image library and draw the generated text on the image using ImageString() function.
![Page 8: Captcha](https://reader036.fdocuments.us/reader036/viewer/2022082804/5490bb1fb479593e0a8b45b3/html5/thumbnails/8.jpg)
by jithin parakka
How to create CAPTCHA
• Now we have CAPTCHA image and its value stored in session variable.
• Compare the value entered by user and value stored in the session variable. Thats it.
![Page 9: Captcha](https://reader036.fdocuments.us/reader036/viewer/2022082804/5490bb1fb479593e0a8b45b3/html5/thumbnails/9.jpg)
by jithin parakka
THANK you