CAPTCHA Image in PHP

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',

                    '3' => '184',
'2' => '177',
                    '4' => '199',

for ($x=0; $x < $this -> winWidth; $x++)
'5' => '255');
.
.
.
{
    for ($y=0; $y < $this -> winHeight; $y++)
    {

         $this -> Colors["$random"], 
$random = mt_rand(0 , 5);
        $temp_color = imagecolorallocate($image, 

}
$this -> Colors["$random"], $this -> Colors["$random"]);
        imagesetpixel( $image, $x, $y , $temp_color );

    }

The result of the above code:

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;
//\\

$random_y = mt_rand(35 , 45);
$char = $this -> Characters[0];
$random_x = mt_rand(10 , 20);

//Writes the given text  into the image using TrueType fonts. 
$random_angle = mt_rand(-20 , 20);

 $char_color, $font, $char);

imagettftext($image, $font_size, $random_angle, $random_x, $random_y,

We repeat it to fill our image with characters.

The result is as follows:

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;

    $xp = $x_period*rand(1,3);
$y_amplitude = 5;
    $x_amplitude = 5;
    

        imagecopy($image, $image, $a-1, sin($k+$a/$xp)*$x_amplitude, 
$k = rand(0,100);
    for ($a = 0; $a<$width; $a++)

    $k = rand(0,100);
$a, 0, 1, $height);
        
    $yp = $y_period*rand(1,2);

        imagecopy($image, $image, sin($k+$a/$yp)*$y_amplitude, 
for ($a = 0; $a<$height; $a++)
         $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:

I've also added some lines to the image :


private $showLine = true;
.
.
.
//draws lines

    for ($i=0; $i<$this->winWidth; $i++ )
if ($this -> showLine)
{
    {

            imageline ( $image, $i, 0, 
if ($i%10 == 0)
        {

            imageline ( $image, $i, 0, 
$i+10, 50, $char_color );

}
$i-10, 50, $char_color );
        }

    }

The latest result:

That's all.

Good luck.

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;

 }
}



?>

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