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Simple PHP CAPTCHA

/ Published in: PHP
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CAPTCHAs are often too hard to solve - hard enough to annoy real human users. This CAPTCHA is easy to understand and to modify and is strong enough to keep out bots whilst being easy on human eyes.

The source code below will not work on its own - it requires a TTF font file and a word list both of which are available in the ZIP archive available for download from the URL given here.

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  1. <?php
  2.  
  3.   function warpedCaptcha($text)
  4.   {
  5.    /*
  6.     this function takes the original captcha text and shuffles
  7. 	the vowels + y around in order to deliver more variable 
  8. 	captcha text
  9.    */
  10.    if (5 > rand(0,6)) return $text;
  11.    //only parttime warping
  12.    $ltrs = array('b'=>'b','c'=>'c','d'=>'d','f'=>'f','g'=>'g','h'=>'h','j'=>'j',
  13.                'k'=>'k','l'=>'l','m'=>'m','n'=>'n','p'=>'p','q'=>'q','r'=>'r',
  14. 			   's'=>'s','t'=>'t','v'=>'v','w'=>'w','x'=>'x','z'=>'z');
  15.  
  16.   $vkeys = $vltrs = explode(',','a,e,i,o,u,y');
  17.   shuffle($vkeys);
  18.   $vowels = array();
  19.   foreach($vkeys as $ndx=>$vkey) $vowels[$vkey] = $vltrs[$ndx];
  20.   //the vowels + y are now jumbled up
  21.  
  22.   $ltrs = array_merge($ltrs,$vowels);
  23.   //full associative array of alphabet with randomized vowels + y
  24.   $text = str_split($text);
  25.  
  26.   $captcha = '';
  27.   foreach($text as $txt) $captcha .= $ltrs[$txt];
  28.   return $captcha;
  29.  }
  30.  
  31.  /*
  32.   xsixlw.txt is a long string of 6 letter words concatenated together.
  33.   We pick a word at random from this text
  34.  */
  35.  $fp = fopen('xsixlw.txt',"r");
  36.  $count = filesize('xsixlw.txt')/6 - 1;
  37.  $pos = 6*rand(0,$count);
  38.  fseek($fp,$pos);
  39.  $captcha = warpedCaptcha(trim(fread($fp,6)));
  40.  fclose($fp);
  41.  
  42.  
  43.  
  44.  session_start();
  45.  $_SESSION['captcha'] = $captcha;
  46.  //store the captcha to check later once the user has solved it
  47.  session_write_close();
  48.  
  49.  $im = imagecreatetruecolor(200,70);//200 x 70 pixel image
  50.  $black = imagecolorallocate($im,0,0,0);
  51.  imagecolortransparent($im,$black);//give it a black background
  52.  
  53.  switch(rand(0,4))
  54.  {
  55.   case 0:$color = imagecolorallocate($im,34,155,91);break;
  56.   case 1:$color = imagecolorallocate($im,233,26,74);break;
  57.   case 2:$color = imagecolorallocate($im,233,26,195);break;
  58.   case 3:$color = imagecolorallocate($im,244,178,19);break;
  59.   case 4:$color = imagecolorallocate($im,53,125,199);break;
  60.  } 
  61.  //pick a random color for the text
  62.  
  63.  $x = 20;$y = 47;//the starting position for drawing
  64.  for ($i=0;$i<6;$i++)
  65.  {
  66.   $angle = rand(-8,8) + rand(0,9)/10;
  67.   $fontsize = rand(22,32);//pick a random font size
  68.   $letter = substr($captcha,$i,1);
  69.   $coords = imagettftext($im,$fontsize,$angle,$x,$y,$color,'oldsans.ttf',$letter);
  70.   //draw each letter
  71.   $x += ($coords[2]-$x) + 1;
  72.  }
  73.  
  74.  
  75. header('Content-type:image/png');
  76. imagepng($im);
  77. imagedestroy($im);
  78. ?>

URL: http://jreply.com/freebies/simplephpcaptcha.html

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