Creating a CAPTCHA with PHP - Check if the user entered the code correctly
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To check if the user entered the code correctly you must first allow the user to do this. You can do this with a simple text form that requires a code to be entered, a simple text field called code or something similar should do nicely. Then you just display the image to the user with a simple <img xsrc="captcha.php" border="0"> tag. It is really too low a level to show you how to make a form like this, if you don't know how to make a form like I described above then this tutorial is probably not for you.
Now assuming that this form has been submitted we need to check if the code matches what was on the image, after all this is the whole point of a captcha system. You can do this in any php file as long as the form described above submits to it. For basic checking we will use the code below.
<?php session_start();
//Encrypt the posted code field and then compare with the stored key
if(md5($_POST['code']) != $_SESSION['key']) { die("Error: You must enter the code correctly"); }else{ echo 'You entered the code correctly'; } ?>
The session_start() you see here simply continues the session from the previous page, easy enough. Then its just a case of simple text matching which you can see is done by the if statement.
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