php generate verification code function_php skills

PHP function to generate verification code, practical and reliable. The rendering of the verification code generated first up and down (the sample effect of the fully digital verification code generated here):

The following is the source code for PHP to generate verification code:

<&#63;php 
session_start(); 
//session_register('CheckCode'); 
//PHP4.2以上版本不需要用session_register()注册SESSION变量 
$type='gif'; 
$width= 45; 
$height= 20; 
header("Content-type: image/".$type); 
srand((double)microtime()*1000000); 
if(isset($_GET['action'])){ 
 $randval=randStr(4,$_GET['action']);  
}else{ 
 $randval=randStr(4,''); 
} 
if($type!='gif'&&function_exists('imagecreatetruecolor')){ 
 $im=@imagecreatetruecolor($width,$height); 
}else{ 
 $im=@imagecreate($width,$height); 
} 
$r=Array(225,211,255,223); 
$g=Array(225,236,237,215); 
$b=Array(225,236,166,125); 
$key=rand(0,3); 
$backColor=ImageColorAllocate($im,$r[$key],$g[$key],$b[$key]);//背景色（随机） 
$borderColor=ImageColorAllocate($im,127,157,185);//边框色 
$pointColor=ImageColorAllocate($im,255,170,255);//点颜色 
@imagefilledrectangle($im,0,0,$width - 1,$height - 1,$backColor);//背景位置 
@imagerectangle($im,0,0,$width-1,$height-1,$borderColor); //边框位置 
$stringColor=ImageColorAllocate($im,255,51,153); 
for($i=0;$i<=100;$i++){ 
 $pointX=rand(2,$width-2); 
 $pointY=rand(2,$height-2); 
 @imagesetpixel($im,$pointX,$pointY,$pointColor); 
} 
@imagestring($im,5,5,1,$randval,$stringColor); 
$ImageFun='Image'.$type; 
$ImageFun($im); 
@imagedestroy($im); 
$_SESSION['CheckCode']=$randval; 
function randStr($len=6,$format='ALL'){ 
 switch($format){ 
  case 'ALL'://生成包含数字和字母的验证码 
   $chars='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'; break; 
  case 'CHAR'://仅生成包含字母的验证码 
   $chars='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz'; break; 
  case 'NUMBER'://仅生成包含数字的验证码 
   $chars='0123456789'; break; 
  default : 
   $chars='ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789'; break; 
 } 
 $string=''; 
 while(strlen($string)<$len) 
 $string.=substr($chars,(mt_rand()%strlen($chars)),1); 
 return $string; 
}

Please see the following example for how to use this function (here is the verification code that generates all numbers):

<img src="checkCode.php&#63;action=NUMBER" width="45" height="20" /> 

The above is the implementation function of how PHP generates verification codes. I hope it will be helpful to everyone's learning.