Using PHP to implement verification code function _php Tutorial

Author: hutuworm Source: Confused and greedy temple
At present, many websites in order to prevent users to use the robot automatic registration, login, irrigation, have adopted a
Verification code technology. The so-called verification Code, is a series of randomly generated numbers or symbols, create a picture,
Images with some interference pixels (to prevent OCR), the user's visual identification of the verification code information, the output
into the form submission site validation, the validation is successful before you can use a feature.

Here we show how to write a PHP program to implement the CAPTCHA function:

Code One:

/*
* Filename:authpage.php
* Author:hutuworm
* date:2003-04-28
* @Copyleft hutuworm.org
*/

Srand (Double) microtime () *1000000);

Verify that the user input is consistent with the verification code
if (isset ($HTTP _post_vars[' authinput '))
{
if (strcmp ($HTTP _post_vars[' Authnum '), $HTTP _post_vars[' authinput ']) ==0)
echo "Verified success! ";
Else
echo "Verification failed! ";
}

Generate a new four-bit integer verification code
while (($authnum =rand ()%10000) <1000);
?>

Code two:

/*
* Filename:authimg.php
* Author:hutuworm
* date:2003-04-28
* @Copyleft hutuworm.org
*/

Generate a Captcha picture
Header ("Content-type:image/png");
Srand (Double) microtime () *1000000);
$im = Imagecreate (58,28);
$black = Imagecolorallocate ($im, 0,0,0);
$white = Imagecolorallocate ($im, 255,255,255);
$gray = Imagecolorallocate ($im, 200,200,200);
Imagefill ($im, 68,30, $gray);

Drawing a four-bit integer verification code into a picture
Imagestring ($im, 5, 8, $HTTP _get_vars[' Authnum '), $black);

for ($i =0; $i <50; $i + +)//Add interfering pixels
{
Imagesetpixel ($im, Rand ()%70, Rand ()%30, $black);
}

Imagepng ($im);
Imagedestroy ($im);
?>

This program runs through the Apache 2.0.45 + PHP 4.3.1 environment.

The above is just a simple implementation of the CAPTCHA function and does not take into account commercial security issues. If you want to enhance security and put this functionality into a commercial application, you can do so in the following few steps:

1. Enable session.
2. Authnum generated in the authimg.php, and calculated md5sum, deposited in session.
3. Authpage.php calculates the results of the validation by comparing the Authinput with the Authnum (md5sum) in the session md5sum.

Site Note: The author uses a simple code to achieve cool features. However, the effect of adding interference pixels is not very good, you can look at the sound of the Rain Forum login Check Code (HTTP://ROR.CN/PERL/UT/USER_LOGIN.CGI), I changed the second paragraph of the code a little bit, generated a similar effect.

The modified code is as follows:

/*
* Filename:authimg.php
* Author:hutuworm
* date:2003-04-28
* @Copyleft hutuworm.org
*/
Generate a Captcha picture
Header ("Content-type:image/png");
Srand (Double) microtime () *1000000);
$im = Imagecreate (62,20);
$black = Imagecolorallocate ($im, 0,0,0);
$white = Imagecolorallocate ($im, 255,255,255);
$gray = Imagecolorallocate ($im, 200,200,200);
Imagefill ($im, 68,30, $gray);
while (($authnum =rand ()%100000) <10000);
Drawing a four-bit integer verification code into a picture
Imagestring ($im, 5, 3, $authnum, $black);
for ($i =0; $i <200; $i + +)//Add interfering pixels
{
$randcolor = Imagecolorallocate ($im, Rand (0,255), Rand (0,255), Rand (0,255));
Imagesetpixel ($im, Rand ()%70, Rand ()%30, $randcolor);
}
Imagepng ($im);
Imagedestroy ($im);
?>

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