This is about how catpcha is working and how to create your own captcha

1. CAPTCHA
How it Works, How to create your
own CAPTCHA
by jithin parakka

2. CAPTCHA
Completely Automated Public Turing test to
tell Computers and Humans Apart
by jithin parakka

3. 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
by jithin parakka

4. 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.
by jithin parakka

5. 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
by jithin parakka

6. 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.
by jithin parakka

7. 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.
by jithin parakka

8. 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.
by jithin parakka

9. THANK you
by jithin parakka