<?php

class TuringImage
{
   // Font Settings
   var $m_szFontFace;
   var $m_iFontSize;
   
   // Image Object
   var $m_oImage;

   // Image Bounds
   var $m_aImageSize;

   // Image Text
   var $m_szImageText;

   function TuringImage()
   {
       // Font Settings
       $this->m_szFontFace = 'fonts/mtcorsva.ttf';
       $this->m_iFontSize  = 20;

       $this->m_oImage = 0;
       $this->m_aImageSize = array( 110, 40 ); // Image Width & Height
       $this->m_szImageText = '';
   }

   function GenerateKey( $iLen )
   {
       $szRandStr = md5( uniqid( rand(), true ) );
       $iRandIdx = rand( 0, (strlen($szRandStr) - $iLen - 1) );
       $szRandStr = substr( $szRandStr, $iRandIdx, $iLen );
       
       // Replace O's and 0's to reduce confusion
       $szRandStr = str_replace( "O", "X", $szRandStr );
       $szRandStr = str_replace( "0", "4", $szRandStr );
       
       $this->m_szImageText = strtoupper( $szRandStr );
       return;
   }

   function GetKey()
   {   return $this->m_szImageText;
   }

   function Create()
   {
       $iTextLen = 5;
       
       // Create Image
       $this->m_oImage = imagecreate( $this->m_aImageSize[0], $this->m_aImageSize[1] );

       // Get Colors
       $oColorFG = imagecolorallocate( $this->m_oImage, 143, 168, 183 );
       $oColorBG = imagecolorallocate( $this->m_oImage, 30, 42, 49 );

       // Set Background Color of Image
       imagefilledrectangle( $this->m_oImage, 0, 0, $this->m_aImageSize[0], $this->m_aImageSize[1], $oColorFG );
       imagefilledrectangle( $this->m_oImage, 1, 1, $this->m_aImageSize[0]-2, $this->m_aImageSize[1]-2, $oColorBG );

       // Obfuscate Image
       $this->ObfuscateImage();
       
       // Write Verification String to Image
       for( $i = 0; $i < $iTextLen; $i++ )
           $this->WriteTTF( (10 + ($i * 18)), (24 + rand(0, 5)), rand(-15, 15), $this->m_szImageText[$i] );
       
       // Output Image to Browser
       imagegif( $this->m_oImage );

       // Free Image Resources
       imagedestroy( $this->m_oImage );
       return;
   }

   function ObfuscateImage()
   {
       $oColor = imagecolorallocate( $this->m_oImage, 143, 168, 183 );
       
       // Random Pixels
       for( $x = 0; $x < $this->m_aImageSize[0]; $x += rand( 3, 7 ) )
           for( $y = 0; $y < $this->m_aImageSize[1]; $y += rand( 3, 7 ) )
               imagesetpixel( $this->m_oImage, $x, $y, $oColor );
       
       // Random Diagonal Lines
       for( $x = 0; $x < $this->m_aImageSize[0]; $x += rand( 15, 25 ) )
           imageline( $this->m_oImage, $x, 0, $x + rand( -50, 50 ), $this->m_aImageSize[1], $oColor );

       for( $y = 0; $y < $this->m_aImageSize[1]; $y += rand( 15, 25 ) )
           imageline( $this->m_oImage, 0, $y, $this->m_aImageSize[0], $y + rand( -50, 50 ), $oColor );

       return;
   }

   function WriteTTF( $iLocX, $iLocY, $iAngle, $szText )
   {
       $oColor = imagecolorallocate( $this->m_oImage, 255, 255, 255 );
       imagettftext( $this->m_oImage, $this->m_iFontSize, $iAngle, $iLocX, $iLocY, $oColor, $this->m_szFontFace, $szText );
   }
}
?>

// Create Turing Test Object
$oTuringTest = new TuringImage();
$oTuringTest->GenerateKey( 5 );  // Length of Key (5)

// Store key in sessions for later comparison
$_SESSION['SECURITY_KEY'] = $oTuringTest->GetKey();

// Set Content Type to GIF with NoCache
header( 'Content-type: image/gif' );
header( 'Expires: ' . gmdate('D, d M Y H:i:s') . 'GMT' );
header( 'Cache-control: no-cache' );

// Output Image
$oTuringTest->Create();