<?php
class Authcode
{
 var $CI;
 var $fontPath;//字體路徑
 var $image;
 var $charLen   = 4; //生成幾位驗(yàn)證碼
 var $arrChr   = array();//驗(yàn)證碼字符
 var $width    = 83; //圖片寬
 var $height   = 24; //圖片高
 var $bgcolor   = "#ffffff"; //背景色
 var $showNoisePix  = true; //生成雜點(diǎn)
 var $noiseNumPix  = 80; //生成雜點(diǎn)數(shù)量
 var $showNoiseLine  = true; //生成雜線
 var $noiseNumLine  = 2; //生成雜線數(shù)量
 var $showBorder  = true; //邊框，當(dāng)雜點(diǎn)、線一起作用的時(shí)候，邊框容易受干擾
 var $borderColor  = "#000000";
 function Authcode()
 {
  $this->CI = & get_instance();
  $this->fontPath = realpath(dirname(__FILE__) . '/fonts/'); //字體文件
  //$this->arrChr   = array_merge(range(1, 9) , range('A', 'Z'));//數(shù)字字母驗(yàn)證碼
  //$this->arrChr   = range('A', 'Z');//純字母驗(yàn)證碼
  $this->arrChr = range(0, 9);//純數(shù)字驗(yàn)證碼
 }
 /**
  * 顯示驗(yàn)證碼
  *
  */
 function show()
 {
  $this->image = imageCreate($this->width, $this->height);
  $this->back = $this->getColor($this->bgcolor);
  imageFilledRectangle($this->image, 0, 0, $this->width, $this->height, $this->back);
  $size = $this->width / $this->charLen - 4;
  if ($size > $this->height) {
   $size = $this->height;
  }
  $left = ($this->width - $this->charLen * ($size + $size / 10)) / $size + 5;
  $code = '';
  for($i = 0; $i < $this->charLen; $i ++) {
   $randKey = rand(0, count($this->arrChr) - 1);
   $randText = $this->arrChr[$randKey];
   $code .= $randText;
   $textColor = imageColorAllocate($this->image, rand(0, 100), rand(0, 100), rand(0, 100));
   $font = $this->fontPath . '/' . rand(1, 5) . ".ttf";
   $randsize = rand($size - $size / 10, $size + $size / 10);
   $location = $left + ($i * $size + $size / 10);
   @imagettftext($this->image, $randsize, rand(- 18, 18), $location, rand($size - $size / 10, $size + $size / 10) + 2, $textColor, $font, $randText);
  }
  if ($this->showNoisePix == true) {
   $this->setNoisePix();
  }
  if ($this->showNoiseLine == true) {
   $this->setNoiseLine();
  }
  if ($this->showBorder == true) {
   $this->borderColor = $this->getColor($this->borderColor);
   imageRectangle($this->image, 0, 0, $this->width - 1, $this->height - 1, $this->borderColor);
  }
  $this->CI->session->set_userdata('auth_code', $code);
  ob_clean();
  header("Content-type: image/jpeg");
  imagejpeg($this->image);
  imagedestroy($this->image);
 }
 /**
  * 顯示驗(yàn)證碼的JS調(diào)用
  *
  */
 function showScript()
 {
  //顯示驗(yàn)證碼
  echo "var img_src = '/imgauthcode/show/?';\n";
  echo "document.writeln('<img id=\"img_authcode\" src=\"' + img_src + Math.random() + '\" style=\"cursor:hand;\" onclick=\"this.src=img_src + Math.random();\" alt=\"點(diǎn)擊更換圖片\">');";
 }
 /**
  * 檢查驗(yàn)證碼是否正確
  *
  * @param string $auth_code
  * @return bool
  */
 function check($auth_code = null)
 {
  return ($this->CI->session->userdata('auth_code') && $auth_code) ? ($this->CI->session->userdata('auth_code') === $auth_code) : false;
 }
 function getColor($color)
 {
  $color = eregi_replace("^#", "", $color);
  $r = $color[0] . $color[1];
  $r = hexdec($r);
  $b = $color[2] . $color[3];
  $b = hexdec($b);
  $g = $color[4] . $color[5];
  $g = hexdec($g);
  $color = imagecolorallocate($this->image, $r, $b, $g);
  return $color;
 }
 function setNoisePix()
 {
  for($i = 0; $i < $this->noiseNumPix; $i ++) {
   $randColor = imageColorAllocate($this->image, rand(0, 255), rand(0, 255), rand(0, 255));
   imageSetPixel($this->image, rand(0, $this->width), rand(0, $this->height), $randColor);
  }
 }
 function setNoiseLine()
 {
  for($i = 0; $i < $this->noiseNumLine; $i ++) {
   $randColor = imageColorAllocate($this->image, rand(0, 255), rand(0, 255), rand(0, 255));
   imageline($this->image, rand(1, $this->width), rand(1, $this->height), rand(1, $this->width), rand(1, $this->height), $randColor);
  }
 }
}

Class Admin extends CI_Controller{
 function __construct()
 {
  parent::__construct();
  $this->load->library('Authcode');
 }
function captcha(){
  if($_POST){
    if ($this->authcode->check($this->input->post('gd_pic'))) {
    echo "right";
   } else {
    echo '驗(yàn)證碼不正確，請(qǐng)重新輸入';
   }
  }else{
   $this->load->view('demo');
  }
 }
 function show_captcha(){ //此方法用于顯示驗(yàn)證碼圖片，歸一個(gè)view中的img的src調(diào)用
  $this->authcode->show();
 }
}

<?php echo form_open('c=admin&m=captcha');?>
<input type="text" name="gd_pic" />
<img src="<?php echo base_url('?c=admin&m=show_captcha');?>" ><br>
<input type="submit" name="submit" value="驗(yàn)證" />
<?php echo form_close();?>