An instance of Captcha verification code class implemented by php

This paper describes the Captcha verification code class implemented by php, which is widely used in php programming. Share it for your reference. The specific methods are as follows:

The verification code class file is as follows:

<?php
/** Captcha  Verification code class 
* Date: 2011-02-19
* Author: fdipzone
*/

class Captcha{ //class start

 private $sname = '';

 public function __construct($sname=''){ // $sname captcha session name
 $this->sname = $sname==''? 'm_captcha' : $sname;
 }

 /**  Generate verification code picture 
 * @param int $length  Verification code length 
 * @param Array $param  In fact, in fact, the 
 * @return IMG
 */
 public function create($length=4,$param=array()){
 Header("Content-type: image/PNG");
 $authnum = $this->random($length); // Generate verification code characters .
 
 $width = isset($param['width'])? $param['width'] : 13; // Text width 
 $height = isset($param['height'])? $param['height'] : 18; // Text height 
 $pnum = isset($param['pnum'])? $param['pnum'] : 100; // Number of interfering pixels 
 $lnum = isset($param['lnum'])? $param['lnum'] : 2; // Number of interfering lines 

 $this->captcha_session($this->sname,$authnum);  // Write random numbers to session

 $pw = $width*$length+10;
 $ph = $height+6;
  
 $im = imagecreate($pw,$ph);   //imagecreate()  Create a new image with the size of  x_size  And  y_size  Gets or sets a blank image of the. 
 $black = ImageColorAllocate($im, 238,238,238); // Set the background color 
 
 $values = array(
  mt_rand(0,$pw), mt_rand(0,$ph),
  mt_rand(0,$pw), mt_rand(0,$ph),
  mt_rand(0,$pw), mt_rand(0,$ph),
  mt_rand(0,$pw), mt_rand(0,$ph),
  mt_rand(0,$pw), mt_rand(0,$ph),
  mt_rand(0,$pw), mt_rand(0,$ph)
 );
 imagefilledpolygon($im, $values, 6, ImageColorAllocate($im, mt_rand(170,255),mt_rand(200,255),mt_rand(210,255))); // Set the interference polygon base map 
 
 /*  Text  */
 for ($i = 0; $i < strlen($authnum); $i++){
  $font = ImageColorAllocate($im, mt_rand(0,50),mt_rand(0,150),mt_rand(0,200));// Set the text color 
  $x = $i/$length * $pw + rand(1, 6); // Set random X Coordinates 
  $y = rand(1, $ph/3);   // Set random Y Coordinates 
  imagestring($im, mt_rand(4,6), $x, $y, substr($authnum,$i,1), $font); 
 }

 /*  Add interfering pixels  */
 for($i=0; $i<$pnum; $i++){
  $dist = ImageColorAllocate($im, mt_rand(0,255),mt_rand(0,255),mt_rand(0,255)); // Set Miscellaneous Color 
  imagesetpixel($im, mt_rand(0,$pw) , mt_rand(0,$ph) , $dist); 
 } 

 /*  Add interference line  */
 for($i=0; $i<$lnum; $i++){
  $dist = ImageColorAllocate($im, mt_rand(50,255),mt_rand(150,255),mt_rand(200,255)); // Set Line Color 
  imageline($im,mt_rand(0,$pw),mt_rand(0,$ph),mt_rand(0,$pw),mt_rand(0,$ph),$dist);
 }

 ImagePNG($im); // With  PNG  Format to output images to browsers or files 
 ImageDestroy($im); // Destruction 1 Image 
 }

 /**  Check the verification code 
 * @param String $captcha  Verification code 
 * @param int $flag  After successful verification,  0: Do not clear session 1: Clear session
 * @return boolean
 */ 
 public function check($captcha,$flag=1){
 if(empty($captcha)){
  return false;
 }else{
  if(strtoupper($captcha)==$this->captcha_session($this->sname)){ // Detection verification code 
  if($flag==1){
   $this->captcha_session($this->sname,'');
  }
  return true;
  }else{
  return false;
  }
 }
 }

 /*  Generate random number function 
 * @param int $length  A randomly generated string is required 
 * @return String
 */
 private function random($length){
 $hash = '';
 $chars = 'ABCDEFGHIJKLMNPQRSTUVWXYZ23456789';
 $max = strlen($chars) - 1;
 for($i = 0; $i < $length; $i++) {
  $hash .= $chars[mt_rand(0, $max)];
 }
 return $hash;
 }

 /**  Verification code session Treatment method 
 * @param String $name captcha session name
 * @param String $value
 * @return String
 */
 private function captcha_session($name,$value=null){
 if(isset($value)){
  if($value!==''){
  $_SESSION[$name] = $value;
  }else{
  unset($_SESSION[$name]);
  }
 }else{
  return isset($_SESSION[$name])? $_SESSION[$name] : '';
 }
 }
} // class end
?>

The demo sample program is as follows:

<?php 
  session_start(); 
  require_once('Captcha.class.php'); 
 
  $obj = new Captcha($sname);   #  Create Captcha Class object  
                  # $sname For saving captcha Adj. session name, Can be left blank , Leave blank as 'm_captcha' 
 
  $obj->create($length,$param);  # Create Captcha And output pictures  
                  # $length For Captcha Length, can be left blank, default is 4 
                  /* $param = array( 
                      'width' => 13    captcha  Character width  
                      'height' => 18    captcha  Character height  
                      'pnum' => 100     Number of interference points 
                      'lnum' => 2      Number of interfering lines  
                      ) 
                       Can be left blank  
                  */ 
  $obj->check($captcha,$flag); #  Check whether the verification code entered by the user is correct, true or false 
                  # $captcha Verification code entered for the user , Required  
                  # $flag  Can be left blank, default to 1  
                  #    1: Automatically clear when verification is successful captcha session 
                  #    0: Do not clear after successful block verification captcha session, Used for ajax Check  
?>

I believe that this paper has a certain reference value for everyone's study of php programming.