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CAPTCHA Image in PHP

By , 23 Feb 2009
 
CAPTCHA.png

Introduction

CAPTCHA (Completely Automated Public Turing test to tell Computers and Humans Apart) image is a way to prevent from bot attacks to our website's forms.
This article demonstrates how we can create our own CAPTCHA.

Using the Code

At first, we have to create a new true color image.
We can create it with imagecreatetruecolor [^] function in PHP.

$image = imagecreatetruecolor($this -> winWidth, 
	$this -> winHeight) //Create a new true color image
	or die("<b>" . __FILE__ . "</b><br />" . __LINE__ . " : " 
    ."Cannot Initialize new GD image stream");
$bg = imagecolorallocate($image, 255, 255, 255);//Allocate a color for an image
imagefill($image, 10, 10, $bg);//Flood fill
.
.
.
return imagepng($image);//Outputs or saves a PNG image from the given $image
imagedestroy($image);//rees any memory associated with image $image

This image is too simple, so we can change the background with a simple algorithm: 

private $Colors =  array (	'0' => '145',
                    '1' => '204',
                    '2' => '177',
                    '3' => '184',
                    '4' => '199',
                    '5' => '255');
.
.
.
for ($x=0; $x < $this -> winWidth; $x++)
{
    for ($y=0; $y < $this -> winHeight; $y++)
    {
        $random = mt_rand(0 , 5);
        $temp_color = imagecolorallocate($image, 
        	$this -> Colors["$random"], 
        	$this -> Colors["$random"], $this -> Colors["$random"]);
        imagesetpixel( $image, $x, $y , $temp_color );
    }
}

The result of the above code:

BG1.png

Then we should write the characters in our image:

//e.g $this->Characters is the string that we're writing in the image
//Font
$font = "tahomabd.ttf";
$font_size = 33;
//\\
$char = $this -> Characters[0];
$random_x = mt_rand(10 , 20);
$random_y = mt_rand(35 , 45);
$random_angle = mt_rand(-20 , 20);
//Writes the given text  into the image using TrueType fonts. 
imagettftext($image, $font_size, $random_angle, $random_x, $random_y, 
	$char_color, $font, $char);

We repeat it to fill our image with characters.
The result is as follows:

CAPTCHA-2.png

But I guess it is a little plain yet, so we can add an effect to our image for creating a more complex CAPTCHA.
I've added a wave effect with a pure mathematic algorithm:

private $applyWave = true;
.
.
.
private function apply_wave($image, $width, $height)
{		
    $x_period = 10;
    $y_period = 10;
    $y_amplitude = 5;
    $x_amplitude = 5;
    
    $xp = $x_period*rand(1,3);
    $k = rand(0,100);
    for ($a = 0; $a<$width; $a++)
        imagecopy($image, $image, $a-1, sin($k+$a/$xp)*$x_amplitude, 
        	$a, 0, 1, $height);
        
    $yp = $y_period*rand(1,2);
    $k = rand(0,100);
    for ($a = 0; $a<$height; $a++)
        imagecopy($image, $image, sin($k+$a/$yp)*$y_amplitude, 
        	$a-1, 0, $a, $width, 1);
    
    return $image;
}

You can change the intensity of waves by changing these variables:

  • $x_period
  • $y_period
  • $y_amplitude
  • $x_amplitude

Let's see the result:

CAPTCHA.png

I've also added some lines to the image : 

private $showLine = true;
.
.
.
//draws lines
if ($this -> showLine)
{
    for ($i=0; $i<$this->winWidth; $i++ )
    {
        if ($i%10 == 0)
        {
            imageline ( $image, $i, 0, 
            	$i+10, 50, $char_color );
            imageline ( $image, $i, 0, 
            	$i-10, 50, $char_color );
        }
    }
}

The latest result:

CAPTCHA-lines.png

That's all.
Good luck.

How To: Using Phpbb3 CAPTCHA
How to: Using PHP Fusion 7 CAPTCHA

Dayyan CAPTCHA Class

Source Code:

<?php
/*
Created by Mohammad Dayyan (C)- 1387/3/2
http://www.mds-soft.persianblog.ir/
*/

if ( !defined('MohammadDayyan') )
{
	die ("Hacking attempt <br /> <b>" . __FILE__ . 
    	"<br /> Line " .  __LINE__  . "</b>" );
	exit;
}

class DayyanConfirmImage
{
	private $showLine = true;
	private $applyWave = true;
	private $winHeight = 50;
	private $winWidth = 320;
	
	private $Characters; // random characters
	
	private $Colors =  array (	'0' => '145',
								'1' => '204',
								'2' => '177',
								'3' => '184',
								'4' => '199',
								'5' => '255');

////////////////////////////////////////////////////////////////////////////////
	public function __construct($ConfirmCode)
	{
		$this -> Characters = $ConfirmCode;
	}

////////////////////////////////////////////////////////////////////////////////
	public function ShowImage()
	{
		//detect server operation system
		if ( strtoupper(substr(PHP_OS, 0, 3)) === 'WIN' )//windows detected
			$this -> win();
		else	//linux detected
			$this -> linux();
	}

////////////////////////////////////////////////////////////////////////////////
	private function win()
	{
		////////////////////////////////////
		//background image
		$image = imagecreatetruecolor($this -> winWidth, $this -> winHeight) 
        	or die("<b>" . __FILE__ . "</b><br />" . __LINE__ . " : 
            	" ."Cannot Initialize new GD image stream");
		$bg = imagecolorallocate($image, 255, 255, 255);
		imagefill($image, 10, 10, $bg);

		for ($x=0; $x < $this -> winWidth; $x++)
		{
			for ($y=0; $y < $this -> winHeight; $y++)
			{
				$random = mt_rand(0 , 5);
				$temp_color = imagecolorallocate($image, 
                	$this -> Colors["$random"], 
                	$this -> Colors["$random"], $this -> Colors["$random"]);
				imagesetpixel( $image, $x, $y , $temp_color );
			}
		}

		$char_color = imagecolorallocatealpha($image, 0, 0, 0, 90);

		//Font
		$font = "tahomabd.ttf";
		$font_size = 33;
		////////////////////////////////////
		//Image characters

		$char = "";

		$char = $this -> Characters[0];
		$random_x = mt_rand(10 , 20);
		$random_y = mt_rand(35 , 45);
		$random_angle = mt_rand(-20 , 20);
		imagettftext($image, $font_size, $random_angle, 
        	$random_x, $random_y, $char_color, $font, $char);

		$char = $this -> Characters[1];
		$random_x = mt_rand(50 , 70);
		$random_y = mt_rand(35 , 45);
		$random_angle = mt_rand(-20 , 20);
		imagettftext($image, $font_size, $random_angle, 
        	$random_x, $random_y, $char_color, $font, $char);

		$char = $this -> Characters[2];
		$random_x = mt_rand(100 , 120);
		$random_y = mt_rand(35 , 45);
		$random_angle = mt_rand(-20 , 20);
		imagettftext($image, $font_size, $random_angle, 
        	$random_x, $random_y, $char_color, $font, $char);

		$char = $this -> Characters[3];
		$random_x = mt_rand(150 , 170);
		$random_y = mt_rand(35 , 45);
		$random_angle = mt_rand(-20 , 20);
		imagettftext($image, $font_size, $random_angle, 
        	$random_x, $random_y, $char_color, $font, $char);

		$char = $this -> Characters[4];
		$random_x = mt_rand(200 , 220);
		$random_y = mt_rand(35 , 45);
		$random_angle = mt_rand(-20 , 20);
		imagettftext($image, $font_size, $random_angle, 
        	$random_x, $random_y, $char_color, $font, $char);

		$char = $this -> Characters[5];
		$random_x = mt_rand(250 , 270);
		$random_y = mt_rand(35 , 45);
		$random_angle = mt_rand(-20 , 20);
		imagettftext($image, $font_size, $random_angle, 
        	$random_x, $random_y, $char_color, $font, $char);

		////////////////////////////////////
		if ($this -> applyWave)
			$image = $this -> apply_wave($image, $this -> winWidth, 
            	$this -> winHeight);
			
		////////////////////////////////////
		//lines
		if ($this -> showLine)
		{
			for ($i=0; $i<$this->winWidth; $i++ )
			{
				if ($i%10 == 0)
				{
					imageline ( $image, $i, 0, 
                    	$i+10, 50, $char_color );
					imageline ( $image, $i, 0, 
                    	$i-10, 50, $char_color );
				}
			}
		}
			
		////////////////////////////////////
		return imagepng($image);
		imagedestroy($image);
	}

/////////////////////////////////////////////////////////////
	private function linux()
	{
		////////////////////////////////////
		//Background image
		$image = imagecreatetruecolor(150, 50) or 
        	die("<b>" . __FILE__ . "</b><br />" . __LINE__ . " : " 
            	."Cannot Initialize new GD image stream");
		$bg = imagecolorallocate($image, 255, 255, 255);
		imagefill($image, 10, 10, $bg);

		for ($x=0; $x < 150; $x++)
		{
			for ($y=0; $y < 50; $y++)
			{
				$random = mt_rand(0 , 5);
				$temp_color = imagecolorallocate($image, $this -> 
                	Colors["$random"], $this -> Colors["$random"], $this -> 
                    Colors["$random"]);
				imagesetpixel( $image, $x, $y , $temp_color );
			}
		}

		$char_color = imagecolorallocatealpha($image, 0, 0, 0, 60);

		////////////////////////////////////
		//Image Info
		$font = 5;

		////////////////////////////////////
		//Image characters
		$char = $this -> Characters[0];
		$random_x = mt_rand(10 , 20);
		$random_y = mt_rand(15,25);
		imagestring($image, $font, $random_x, $random_y, $char, $char_color);

		$char = $this -> Characters[1];
		$random_x = mt_rand(30 , 40);
		$random_y = mt_rand(15,25);
		imagestring($image, $font, $random_x, $random_y, $char, $char_color);

		$char = $this -> Characters[2];
		$random_x = mt_rand(50 , 60);
		$random_y = mt_rand(15,25);
		imagestring($image, $font, $random_x, $random_y, $char, $char_color);

		$char = $this -> Characters[3];
		$random_x = mt_rand(70 , 80);
		$random_y = mt_rand(15,25);
		imagestring($image, $font, $random_x, $random_y, $char, $char_color);

		$char = $this -> Characters[4];
		$random_x = mt_rand(90 , 100);
		$random_y = mt_rand(15,25);
		imagestring($image, $font, $random_x, $random_y, $char, $char_color);

		$char = $this -> Characters[5];
		$random_x = mt_rand(110 , 120);
		$random_y = mt_rand(15,25);
		imagestring($image, $font, $random_x, $random_y, $char, $char_color);

		///////////////////////
		return imagepng($image);
		imagedestroy($image);
	}

///////////////////////////////////////////////////////////
	private function apply_wave($image, $width, $height)
	{		
		$x_period = 10;
		$y_period = 10;
		$y_amplitude = 5;
		$x_amplitude = 5;
		
		$xp = $x_period*rand(1,3);
		$k = rand(0,100);
		for ($a = 0; $a<$width; $a++)
			imagecopy($image, $image, $a-1, sin($k+$a/$xp)*$x_amplitude, 
            	$a, 0, 1, $height);
			
		$yp = $y_period*rand(1,2);
		$k = rand(0,100);
		for ($a = 0; $a<$height; $a++)
			imagecopy($image, $image, sin($k+$a/$yp)*$y_amplitude, 
            	$a-1, 0, $a, $width, 1);
		
		return $image;
	}
}

?>

History

  • 3rd January, 2008: First post
  • 23rd February, 2009: Last update

License

This article, along with any associated source code and files, is licensed under The GNU General Public License (GPLv3)

About the Author

 Mohammad Dayyan
Iran (Islamic Republic Of) Iran (Islamic Republic Of)
Member
No Biography provided

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QuestionNeed some HelpmemberMember 961824821 Nov '12 - 1:29 
Questiongoodmemberajjaj16 May '12 - 20:01 
QuestionWindows <--> Linux and further improving securitymemberTerraD2 Apr '12 - 1:05 
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QuestionHow does the code against hacking attempts work? [modified]memberTerraD1 Apr '12 - 22:15 
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About Article
This article demonstrates how we can create a CAPTCHA image with PHP
Type Article
Licence GPL3
First Posted 2 Jun 2008
Views 38,738
Downloads 1,568
Bookmarked 32 times
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